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• Sniffing out SQL Code Smells: Inconsistent use of Symbolic names and Datatypes

  - by Phil Factor

  It is an awkward feeling. You’ve just delivered a database application that seems to be working fine in production, and you just run a few checks on it. You discover that there is a potential bug that, out of sheer good chance, hasn’t kicked in to produce an error; but it lurks, like a smoking bomb. Worse, maybe you find that the bug has started its evil work of corrupting the data, but in ways that nobody has, so far detected. You investigate, and find the damage. You are somehow going to have to repair it. Yes, it still very occasionally happens to me. It is not a nice feeling, and I do anything I can to prevent it happening. That’s why I’m interested in SQL code smells. SQL Code Smells aren’t necessarily bad practices, but just show you where to focus your attention when checking an application. Sometimes with databases the bugs can be subtle. SQL is rather like HTML: the language does its best to try to carry out your wishes, rather than to be picky about your bugs. Most of the time, this is a great benefit, but not always. One particular place where this can be detrimental is where you have implicit conversion between different data types. Most of the time it is completely harmless but we’re  concerned about the occasional time it isn’t. Let’s give an example: String truncation. Let’s give another even more frightening one, rounding errors on assignment to a number of different precision. Each requires a blog-post to explain in detail and I’m not now going to try. Just remember that it is not always a good idea to assign data to variables, parameters or even columns when they aren’t the same datatype, especially if you are relying on implicit conversion to work its magic.For details of the problem and the consequences, see here:  SR0014: Data loss might occur when casting from {Type1} to {Type2} . For any experienced Database Developer, this is a more frightening read than a Vampire Story. This is why one of the SQL Code Smells that makes me edgy, in my own or other peoples’ code, is to see parameters, variables and columns that have the same names and different datatypes. Whereas quite a lot of this is perfectly normal and natural, you need to check in case one of two things have gone wrong. Either sloppy naming, or mixed datatypes. Sure it is hard to remember whether you decided that the length of a log entry was 80 or 100 characters long, or the precision of a number. That is why a little check like this I’m going to show you is excellent for tidying up your code before you check it back into source Control! 1/ Checking Parameters only If you were just going to check parameters, you might just do this. It simply groups all the parameters, either input or output, of all the routines (e.g. stored procedures or functions) by their name and checks to see, in the HAVING clause, whether their data types are all the same. If not, it lists all the examples and their origin (the routine) Even this little check can occasionally be scarily revealing. ;WITH userParameter AS  ( SELECT   c.NAME AS ParameterName,  OBJECT_SCHEMA_NAME(c.object_ID) + '.' + OBJECT_NAME(c.object_ID) AS ObjectName,  t.name + ' '     + CASE     --we may have to put in the length            WHEN t.name IN ('char', 'varchar', 'nchar', 'nvarchar')             THEN '('               + CASE WHEN c.max_length = -1 THEN 'MAX'                ELSE CONVERT(VARCHAR(4),                    CASE WHEN t.name IN ('nchar', 'nvarchar')                      THEN c.max_length / 2 ELSE c.max_length                    END)                END + ')'         WHEN t.name IN ('decimal', 'numeric')             THEN '(' + CONVERT(VARCHAR(4), c.precision)                   + ',' + CONVERT(VARCHAR(4), c.Scale) + ')'         ELSE ''      END  --we've done with putting in the length      + CASE WHEN XML_collection_ID <> 0         THEN --deal with object schema names             '(' + CASE WHEN is_XML_Document = 1                    THEN 'DOCUMENT '                    ELSE 'CONTENT '                   END              + COALESCE(               (SELECT QUOTENAME(ss.name) + '.' + QUOTENAME(sc.name)                FROM sys.xml_schema_collections sc                INNER JOIN Sys.Schemas ss ON sc.schema_ID = ss.schema_ID                WHERE sc.xml_collection_ID = c.XML_collection_ID),'NULL') + ')'          ELSE ''         END        AS [DataType]  FROM sys.parameters c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID  WHERE OBJECT_SCHEMA_NAME(c.object_ID) <> 'sys'   AND parameter_id>0)SELECT CONVERT(CHAR(80),objectName+'.'+ParameterName),DataType FROM UserParameterWHERE ParameterName IN   (SELECT ParameterName FROM UserParameter    GROUP BY ParameterName    HAVING MIN(Datatype)<>MAX(DataType))ORDER BY ParameterName   so, in a very small example here, we have a @ClosingDelimiter variable that is only CHAR(1) when, by the looks of it, it should be up to ten characters long, or even worse, a function that should be a char(1) and seems to let in a string of ten characters. Worth investigating. Then we have a @Comment variable that can't decide whether it is a VARCHAR(2000) or a VARCHAR(MAX) 2/ Columns and Parameters Actually, once we’ve cleared up the mess we’ve made of our parameter-naming in the database we’re inspecting, we’re going to be more interested in listing both columns and parameters. We can do this by modifying the routine to list columns as well as parameters. Because of the slight complexity of creating the string version of the datatypes, we will create a fake table of both columns and parameters so that they can both be processed the same way. After all, we want the datatypes to match Unfortunately, parameters do not expose all the attributes we are interested in, such as whether they are nullable (oh yes, subtle bugs happen if this isn’t consistent for a datatype). We’ll have to leave them out for this check. Voila! A slight modification of the first routine ;WITH userObject AS  ( SELECT   Name AS DataName,--the actual name of the parameter or column ('@' removed)  --and the qualified object name of the routine  OBJECT_SCHEMA_NAME(ObjectID) + '.' + OBJECT_NAME(ObjectID) AS ObjectName,  --now the harder bit: the definition of the datatype.  TypeName + ' '     + CASE     --we may have to put in the length. e.g. CHAR (10)           WHEN TypeName IN ('char', 'varchar', 'nchar', 'nvarchar')             THEN '('               + CASE WHEN MaxLength = -1 THEN 'MAX'                ELSE CONVERT(VARCHAR(4),                    CASE WHEN TypeName IN ('nchar', 'nvarchar')                      THEN MaxLength / 2 ELSE MaxLength                    END)                END + ')'         WHEN TypeName IN ('decimal', 'numeric')--a BCD number!             THEN '(' + CONVERT(VARCHAR(4), Precision)                   + ',' + CONVERT(VARCHAR(4), Scale) + ')'         ELSE ''      END  --we've done with putting in the length      + CASE WHEN XML_collection_ID <> 0 --tush tush. XML         THEN --deal with object schema names             '(' + CASE WHEN is_XML_Document = 1                    THEN 'DOCUMENT '                    ELSE 'CONTENT '                   END              + COALESCE(               (SELECT TOP 1 QUOTENAME(ss.name) + '.' + QUOTENAME(sc.Name)                FROM sys.xml_schema_collections sc                INNER JOIN Sys.Schemas ss ON sc.schema_ID = ss.schema_ID                WHERE sc.xml_collection_ID = XML_collection_ID),'NULL') + ')'          ELSE ''         END        AS [DataType],       DataObjectType  FROM   (Select t.name AS TypeName, REPLACE(c.name,'@','') AS Name,          c.max_length AS MaxLength, c.precision AS [Precision],           c.scale AS [Scale], c.[Object_id] AS ObjectID, XML_collection_ID,          is_XML_Document,'P' AS DataobjectType  FROM sys.parameters c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID  AND parameter_id>0  UNION all  Select t.name AS TypeName, c.name AS Name, c.max_length AS MaxLength,          c.precision AS [Precision], c.scale AS [Scale],          c.[Object_id] AS ObjectID, XML_collection_ID,is_XML_Document,          'C' AS DataobjectType            FROM sys.columns c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID   WHERE OBJECT_SCHEMA_NAME(c.object_ID) <> 'sys'  )f)SELECT CONVERT(CHAR(80),objectName+'.'   + CASE WHEN DataobjectType ='P' THEN '@' ELSE '' END + DataName),DataType FROM UserObjectWHERE DataName IN   (SELECT DataName FROM UserObject   GROUP BY DataName    HAVING MIN(Datatype)<>MAX(DataType))ORDER BY DataName     Hmm. I can tell you I found quite a few minor issues with the various tabases I tested this on, and found some potential bugs that really leap out at you from the results. Here is the start of the result for AdventureWorks. Yes, AccountNumber is, for some reason, a Varchar(10) in the Customer table. Hmm. odd. Why is a city fifty characters long in that view?  The idea of the description of a colour being 256 characters long seems over-ambitious. Go down the list and you'll spot other mistakes. There are no bugs, but just mess. We started out with a listing to examine parameters, then we mixed parameters and columns. Our last listing is for a slightly more in-depth look at table columns. You’ll notice that we’ve delibarately removed the indication of whether a column is persisted, or is an identity column because that gives us false positives for our code smells. If you just want to browse your metadata for other reasons (and it can quite help in some circumstances) then uncomment them! ;WITH userColumns AS  ( SELECT   c.NAME AS columnName,  OBJECT_SCHEMA_NAME(c.object_ID) + '.' + OBJECT_NAME(c.object_ID) AS ObjectName,  REPLACE(t.name + ' '   + CASE WHEN is_computed = 1 THEN ' AS ' + --do DDL for a computed column          (SELECT definition FROM sys.computed_columns cc           WHERE cc.object_id = c.object_id AND cc.column_ID = c.column_ID)     --we may have to put in the length            WHEN t.Name IN ('char', 'varchar', 'nchar', 'nvarchar')             THEN '('               + CASE WHEN c.Max_Length = -1 THEN 'MAX'                ELSE CONVERT(VARCHAR(4),                    CASE WHEN t.Name IN ('nchar', 'nvarchar')                      THEN c.Max_Length / 2 ELSE c.Max_Length                    END)                END + ')'       WHEN t.name IN ('decimal', 'numeric')       THEN '(' + CONVERT(VARCHAR(4), c.precision) + ',' + CONVERT(VARCHAR(4), c.Scale) + ')'       ELSE ''      END + CASE WHEN c.is_rowguidcol = 1          THEN ' ROWGUIDCOL'          ELSE ''         END + CASE WHEN XML_collection_ID <> 0            THEN --deal with object schema names             '(' + CASE WHEN is_XML_Document = 1                THEN 'DOCUMENT '                ELSE 'CONTENT '               END + COALESCE((SELECT                QUOTENAME(ss.name) + '.' + QUOTENAME(sc.name)                FROM                sys.xml_schema_collections sc                INNER JOIN Sys.Schemas ss ON sc.schema_ID = ss.schema_ID                WHERE                sc.xml_collection_ID = c.XML_collection_ID),                'NULL') + ')'            ELSE ''           END + CASE WHEN is_identity = 1             THEN CASE WHEN OBJECTPROPERTY(object_id,                'IsUserTable') = 1 AND COLUMNPROPERTY(object_id,                c.name,                'IsIDNotForRepl') = 0 AND OBJECTPROPERTY(object_id,                'IsMSShipped') = 0                THEN ''                ELSE ' NOT FOR REPLICATION '               END             ELSE ''            END + CASE WHEN c.is_nullable = 0               THEN ' NOT NULL'               ELSE ' NULL'              END + CASE                WHEN c.default_object_id <> 0                THEN ' DEFAULT ' + object_Definition(c.default_object_id)                ELSE ''               END + CASE                WHEN c.collation_name IS NULL                THEN ''                WHEN c.collation_name <> (SELECT                collation_name                FROM                sys.databases                WHERE                name = DB_NAME()) COLLATE Latin1_General_CI_AS                THEN COALESCE(' COLLATE ' + c.collation_name,                '')                ELSE ''                END,'  ',' ') AS [DataType]FROM sys.columns c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID  WHERE OBJECT_SCHEMA_NAME(c.object_ID) <> 'sys')SELECT CONVERT(CHAR(80),objectName+'.'+columnName),DataType FROM UserColumnsWHERE columnName IN (SELECT columnName FROM UserColumns  GROUP BY columnName  HAVING MIN(Datatype)<>MAX(DataType))ORDER BY columnName If you take a look down the results against Adventureworks, you'll see once again that there are things to investigate, mostly, in the illustration, discrepancies between null and non-null datatypes So I here you ask, what about temporary variables within routines? If ever there was a source of elusive bugs, you'll find it there. Sadly, these temporary variables are not stored in the metadata so we'll have to find a more subtle way of flushing these out, and that will, I'm afraid, have to wait!

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• The Excel Column Name assigment problem

  - by Peter Larsson

  Here is a generic algorithm to get the Excel column name according to it's position. By changing the @Base parameter, you can do this for any sequence according to same style as Excel. DECLARE @Value INT = 8839,         @Base TINYINT = 26   ;WITH cteSequence(Value, Delta, Quote, Base, Chr) AS (     SELECT  CAST(@Value AS INT) AS Value,             CAST(1 AS INT) AS Delta,             CAST(@Base AS INT) AS Quote,             CAST(@Base AS INT) AS Base,             CHAR(65 +(@Value - 1) % @Base) AS Chr       UNION ALL       SELECT  Value AS Value,             Quote AS Delta,             26 * Quote AS Quote,             Base AS Base,             CHAR(65 +((Value - Delta)/ Quote - 1) % Base) AS Chr     FROM    cteSequence     WHERE   CHAR(65 +((Value - Delta)/ Quote - 1) % Base) <> '@' ) SELECT  CAST(Msg AS VARCHAR(MAX)) FROM    (             SELECT        '' + Chr             FROM        cteSequence             ORDER BY    Delta DESC             FOR XML        PATH('')         ) AS x(Msg)

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• Should *'s go next to the type or the variable name? [closed]

  - by derekerdmann

  Possible Duplicate: int* i; or int *i; or int * i; When working in C or C++, how should pointers be declared? Like this: char* derp; or this: char *derp; I typically use the first method, because the variable is a character pointer, but I know that it can create confusion when declaring multiple variables at once: char* herp, derp; herp becomes a character pointer, while derp is just a character. I know it often comes down to coding style, but which one is "better?" Should I sacrifice clarity to eliminate potential confusion?

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• Functions returning pointers

  - by fg nu

  C++ noob here. I have a very basic question about a construct I found in the C++ book I am reading. // class declaration class CStr { char sData[256]; public: char* get(void); }; // implementation of the function char* CStr::get(void) { return sData; } So the Cstr::get function is obviously meant to return a character pointer, but the function is passing what looks like the value (return sData). Does C++ know to return the address of the returned object? My guess would have been that the function definition would be return &sData.

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• Should functions of a C library always expect a string's length?

  - by Benjamin Kloster

  I'm currently working on a library written in C. Many functions of this library expect a string as char* or const char* in their arguments. I started out with those functions always expecting the string's length as a size_t so that null-termination wasn't required. However, when writing tests, this resulted in frequent use of strlen(), like so: const char* string = "Ugh, strlen is tedious"; libFunction(string, strlen(string)); Trusting the user to pass properly terminated strings would lead to less safe, but more concise and (in my opinion) readable code: libFunction("I hope there's a null-terminator there!"); So, what's the sensible practice here? Make the API more complicated to use, but force the user to think of their input, or document the requirement for a null-terminated string and trust the caller?

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• indicator-chars doesn't work on Oneiric

  - by Lucio

  I downloaded Indicator-Char and unzipped the files. I added the characters there I wanted perfectly. When I run the python script it loads the daemon and I can see this characters. But the problem is that when I click on them, not copied anything to the clipboard. I see the code where is the copy function, is the following. def on_char_click(self, widget, char): cb = gtk.Clipboard(selection="PRIMARY") cb.set_text(char) Is a syntax problem? There is a problem on my system?

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• Array of pointers in C++.

  - by Theorem

  I am not understanding the output of this , #include <iostream> using namespace std; // pointers and arrays char ch1 = 'a' , ch2= 'b'; char ch3[6] = {'c', 'd', 'e', 'f', 'g' , 'h'}; char *ptr[3]; int main () { ptr[0] = &ch1 ; ptr[2] = ch3; cout << &ch1 << endl; } The out put is abcdefgh . isn't &ch1 supposed to give the address of ch1 ? I cannot make sense why the output should be abcdefgh.

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• What is wrong with this code for reading binary files? [on hold]

  - by qed

  What is wrong with this code for reading binary files? It compiles OK, but will not print out the file as planned, in fact, it prints nothing at all. #include <iostream> #include <fstream> int main(int argc, const char *argv[]) { if (argc < 2) { ::std::cerr << "usage: " << argv[0] << " <filename>\n"; return 1; } ::std::basic_ifstream<unsigned char> in(argv[1], ::std::ios::binary); unsigned char uc; while (in.get(uc)) { printf("%02X ", uc); } // TODO: error handling, in case the file could not be opened or read return 0; }

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• how can I specify interleaved vertex attributes and vertex indices

  - by freefallr

  I'm writing a generic ShaderProgram class that compiles a set of Shader objects, passes args to the shader (like vertex position, vertex normal, tex coords etc), then links the shader components into a shader program, for use with glDrawArrays. My vertex data already exists in a VertexBufferObject that uses the following data structure to create a vertex buffer: class CustomVertex { public: float m_Position[3]; // x, y, z // offset 0, size = 3*sizeof(float) float m_TexCoords[2]; // u, v // offset 3*sizeof(float), size = 2*sizeof(float) float m_Normal[3]; // nx, ny, nz; float colour[4]; // r, g, b, a float padding[20]; // padded for performance }; I've already written a working VertexBufferObject class that creates a vertex buffer object from an array of CustomVertex objects. This array is said to be interleaved. It renders successfully with the following code: void VertexBufferObject::Draw() { if( ! m_bInitialized ) return; glBindBuffer( GL_ARRAY_BUFFER, m_nVboId ); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, m_nVboIdIndex ); glEnableClientState( GL_VERTEX_ARRAY ); glEnableClientState( GL_TEXTURE_COORD_ARRAY ); glEnableClientState( GL_NORMAL_ARRAY ); glEnableClientState( GL_COLOR_ARRAY ); glVertexPointer( 3, GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 0) ); glTexCoordPointer(3, GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 12)); glNormalPointer(GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 20)); glColorPointer(3, GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 32)); glDrawElements( GL_TRIANGLES, m_nNumIndices, GL_UNSIGNED_INT, ((char*)NULL + 0) ); glDisableClientState( GL_VERTEX_ARRAY ); glDisableClientState( GL_TEXTURE_COORD_ARRAY ); glDisableClientState( GL_NORMAL_ARRAY ); glDisableClientState( GL_COLOR_ARRAY ); glBindBuffer( GL_ARRAY_BUFFER, 0 ); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, 0 ); } Back to the Vertex Array Object though. My code for creating the Vertex Array object is as follows. This is performed before the ShaderProgram runtime linking stage, and no glErrors are reported after its steps. // Specify the shader arg locations (e.g. their order in the shader code) for( int n = 0; n < vShaderArgs.size(); n ++) glBindAttribLocation( m_nProgramId, n, vShaderArgs[n].sFieldName.c_str() ); // Create and bind to a vertex array object, which stores the relationship between // the buffer and the input attributes glGenVertexArrays( 1, &m_nVaoHandle ); glBindVertexArray( m_nVaoHandle ); // Enable the vertex attribute array (we're using interleaved array, since its faster) glBindBuffer( GL_ARRAY_BUFFER, vShaderArgs[0].nVboId ); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, vShaderArgs[0].nVboIndexId ); // vertex data for( int n = 0; n < vShaderArgs.size(); n ++ ) { glEnableVertexAttribArray(n); glVertexAttribPointer( n, vShaderArgs[n].nFieldSize, GL_FLOAT, GL_FALSE, vShaderArgs[n].nStride, (GLubyte *) NULL + vShaderArgs[n].nFieldOffset ); AppLog::Ref().OutputGlErrors(); } This doesn't render correctly at all. I get a pattern of white specks onscreen, in the shape of the terrain rectangle, but there are no regular lines etc. Here's the code I use for rendering: void ShaderProgram::Draw() { using namespace AntiMatter; if( ! m_nShaderProgramId || ! m_nVaoHandle ) { AppLog::Ref().LogMsg("ShaderProgram::Draw() Couldn't draw object, as initialization of ShaderProgram is incomplete"); return; } glUseProgram( m_nShaderProgramId ); glBindVertexArray( m_nVaoHandle ); glDrawArrays( GL_TRIANGLES, 0, m_nNumTris ); glBindVertexArray(0); glUseProgram(0); } Can anyone see errors or omissions in either the VAO creation code or rendering code? thanks!

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• Detect Unicode Usage in SQL Column

  One optimization you can make to a SQL table that is overly large is to change from nvarchar (or nchar) to varchar (or char).  Doing so will cut the size used by the data in half, from 2 bytes per character (+ 2 bytes of overhead for varchar) to only 1 byte per character.  However, you will lose the ability to store Unicode characters, such as those used by many non-English alphabets.  If the tables are storing user-input, and your application is or might one day be used internationally, its likely that using Unicode for your characters is a good thing.  However, if instead the data is being generated by your application itself or your development team (such as lookup data), and you can be certain that Unicode character sets are not required, then switching such columns to varchar/char can be an easy improvement to make. Avoid Premature Optimization If you are working with a lookup table that has a small number of rows, and is only ever referenced in the application by its numeric ID column, then you wont see any benefit to using varchar vs. nvarchar.  More generally, for small tables, you wont see any significant benefit.  Thus, if you have a general policy in place to use nvarchar/nchar because it offers more flexibility, do not take this post as a recommendation to go against this policy anywhere you can.  You really only want to act on measurable evidence that suggests that using Unicode is resulting in a problem, and that you wont lose anything by switching to varchar/char. Obviously the main reason to make this change is to reduce the amount of space required by each row.  This in turn affects how many rows SQL Server can page through at a time, and can also impact index size and how much disk I/O is required to respond to queries, etc.  If for example you have a table with 100 million records in it and this table has a column of type nchar(5), this column will use 5 * 2 = 10 bytes per row, and with 100M rows that works out to 10 bytes * 100 million = 1000 MBytes or 1GB.  If it turns out that this column only ever stores ASCII characters, then changing it to char(5) would reduce this to 5*1 = 5 bytes per row, and only 500MB.  Of course, if it turns out that it only ever stores the values true and false then you could go further and replace it with a bit data type which uses only 1 byte per row (100MB  total). Detecting Whether Unicode Is In Use So by now you think that you have a problem and that it might be alleviated by switching some columns from nvarchar/nchar to varchar/char but youre not sure whether youre currently using Unicode in these columns.  By definition, you should only be thinking about this for a column that has a lot of rows in it, since the benefits just arent there for a small table, so you cant just eyeball it and look for any non-ASCII characters.  Instead, you need a query.  Its actually very simple: SELECT DISTINCT(CategoryName)FROM CategoriesWHERE CategoryName <> CONVERT(varchar, CategoryName) Summary Gregg Stark for the tip. Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• "Gtk-WARNING **: cannot open display: " when using execve to launch a Gtk program on ubuntu

  - by michael

  Hi, I have the following c program which launches a Gtk Program on ubuntu: #include <unistd.h> int main( int argc, const char* argv[] ) { char *args[2] = { "testarg", 0 }; char *envp[1] = { 0 }; execve("/home/michael/MyGtkApp",args,envp); } I get "Gtk-WARNING **: cannot open display: " and my program is not launched. I have tried setting char *envp[1] = {"DISPLAY:0.0"}; and execute 'xhost +' , I dont' see the 'cannot open display' warning, but my program is still not launched. Does anyone know how to fix my problem? Thank you.

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• Strings in Objective-C++

  - by John Smith

  I just switched my code from Objective-C to Objective-C++. Everything goes swimmingly except for two lines. NSString * text1=[[NSString stringWithFormat:@"%.2f",ymax] UTF8String]; This line complains that error: cannot convert 'const char*' to 'NSString*' in initialization The second error related to the first is from the line: CGContextShowTextAtPoint(context, 2, 8, text1, strlen(text1)); It complains that error: cannot convert 'NSString*' to 'const char*' for argument '1' to 'size_t strlen(const char*)' Is there something I missed in the differences between ObjC and ObjC++?

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• Write a signal handler to catch SIGSEGV

  - by Adi

  Hi all, I want to write a signal handler to catch SIGSEGV. First , I would protect a block of memory for read or writes using char *buffer; char *p; char a; int pagesize = 4096; " mprotect(buffer,pagesize,PROT_NONE) " What this will do is , it will protect the memory starting from buffer till pagesize for any reads or writes. Second , I will try to read the memory by doing something like p = buffer; a = *p This will generate a SIGSEGV and i have initialized a handler for this. The handler will be called . So far so good. Now the problem I am facing is , once the handler is called, I want to change the access write of the memory by doing mprotect(buffer, pagesize,PROT_READ); and continue my normal functioning of the code. I do not want to exit the function. On future writes to the same memory, I want again catch the signal and modify the write rights and then take account of that event. Here is the code I am trying : #include <signal.h> #include <stdio.h> #include <malloc.h> #include <stdlib.h> #include <errno.h> #include <sys/mman.h> #define handle_error(msg) \ do { perror(msg); exit(EXIT_FAILURE); } while (0) char *buffer; int flag=0; static void handler(int sig, siginfo_t *si, void *unused) { printf("Got SIGSEGV at address: 0x%lx\n",(long) si->si_addr); printf("Implements the handler only\n"); flag=1; //exit(EXIT_FAILURE); } int main(int argc, char *argv[]) { char *p; char a; int pagesize; struct sigaction sa; sa.sa_flags = SA_SIGINFO; sigemptyset(&sa.sa_mask); sa.sa_sigaction = handler; if (sigaction(SIGSEGV, &sa, NULL) == -1) handle_error("sigaction"); pagesize=4096; /* Allocate a buffer aligned on a page boundary; initial protection is PROT_READ | PROT_WRITE */ buffer = memalign(pagesize, 4 * pagesize); if (buffer == NULL) handle_error("memalign"); printf("Start of region: 0x%lx\n", (long) buffer); printf("Start of region: 0x%lx\n", (long) buffer+pagesize); printf("Start of region: 0x%lx\n", (long) buffer+2*pagesize); printf("Start of region: 0x%lx\n", (long) buffer+3*pagesize); //if (mprotect(buffer + pagesize * 0, pagesize,PROT_NONE) == -1) if (mprotect(buffer + pagesize * 0, pagesize,PROT_NONE) == -1) handle_error("mprotect"); //for (p = buffer ; ; ) if(flag==0) { p = buffer+pagesize/2; printf("It comes here before reading memory\n"); a = *p; //trying to read the memory printf("It comes here after reading memory\n"); } else { if (mprotect(buffer + pagesize * 0, pagesize,PROT_READ) == -1) handle_error("mprotect"); a = *p; printf("Now i can read the memory\n"); } /* for (p = buffer;p<=buffer+4*pagesize ;p++ ) { //a = *(p); *(p) = 'a'; printf("Writing at address %p\n",p); }*/ printf("Loop completed\n"); /* Should never happen */ exit(EXIT_SUCCESS); } The problem I am facing with this is ,only the signal handler is running and I am not able to return to the main function after catching the signal.. Any help in this will be greatly appreciated. Thanks in advance Aditya

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• How to use custom masks in MaskedEditExtender?

  - by bastos.sergio

  Hello, I need to create a textbox which accepts 3 chars and must follow the following format 1st char - only numbers 2nd char - only upper case letters 3rd char - numbers and upper case letters (except zero) This is what I have so far, but it's not working <ajaxToolkit:MaskedEditExtender ID="MaskedEditExtender1" runat="server" Mask="9L9" TargetControlID="txtNUIPC3" PromptCharacter=""> </ajaxToolkit:MaskedEditExtender>

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• the sizeof why ??!!

  - by hiba salem

  hi I hve this code struct Student { char name[48]; float grade; int marks[10,5]; char gender; }; Student s; Now I have to get the sizeof s so i added printf("%d",sizeof(s)); now when I hit compile the result showing is 256 and its wrong because it shoud be 253 as because the size of char name[48]; ---- 48 and float grade; ----- 4 and int marks[10,5]; ------ 200 and char gender; -------1 so 48+4+200+1 = 253 so why its telling me 256 ??

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• Creating a MiniDump of a running process

  - by Lodle

  Im trying to make a tool for my end users that can create a MiniDump of my application if it hangs (i.e. external to the app). Im using the same code as the internal MiniDumper but with the handle and processid of the app but i keep getting error code 0xD0000024 when calling MiniDumpWriteDump. Any ideas? void produceDump( const char* exe ) { DWORD processId = 0; HANDLE process = findProcess(exe, processId); if (!process || processId == 0) { printf("Unable to find exe %s to produce dump.\n", exe); return; } LONG retval = EXCEPTION_CONTINUE_SEARCH; HWND hParent = NULL; // find a better value for your app // firstly see if dbghelp.dll is around and has the function we need // look next to the EXE first, as the one in System32 might be old // (e.g. Windows 2000) HMODULE hDll = NULL; char szDbgHelpPath[_MAX_PATH]; if (GetModuleFileName( NULL, szDbgHelpPath, _MAX_PATH )) { char *pSlash = _tcsrchr( szDbgHelpPath, '\\' ); if (pSlash) { _tcscpy( pSlash+1, "DBGHELP.DLL" ); hDll = ::LoadLibrary( szDbgHelpPath ); } } if (hDll==NULL) { // load any version we can hDll = ::LoadLibrary( "DBGHELP.DLL" ); } LPCTSTR szResult = NULL; int err = 0; if (hDll) { MINIDUMPWRITEDUMP pDump = (MINIDUMPWRITEDUMP)::GetProcAddress( hDll, "MiniDumpWriteDump" ); if (pDump) { char szDumpPath[_MAX_PATH]; char szScratch [_MAX_PATH]; time_t rawtime; struct tm * timeinfo; time ( &rawtime ); timeinfo = localtime ( &rawtime ); char comAppPath[MAX_PATH]; SHGetFolderPath(NULL, CSIDL_COMMON_APPDATA , NULL, SHGFP_TYPE_CURRENT, comAppPath ); //COMMONAPP_PATH _snprintf(szDumpPath, _MAX_PATH, "%s\\DN", comAppPath); CreateDirectory(szDumpPath, NULL); _snprintf(szDumpPath, _MAX_PATH, "%s\\DN\\D", comAppPath); CreateDirectory(szDumpPath, NULL); _snprintf(szDumpPath, _MAX_PATH, "%s\\DN\\D\\dumps", comAppPath); CreateDirectory(szDumpPath, NULL); char fileName[_MAX_PATH]; _snprintf(fileName, _MAX_PATH, "%s_Dump_%04d%02d%02d_%02d%02d%02d.dmp", exe, timeinfo->tm_year+1900, timeinfo->tm_mon, timeinfo->tm_mday, timeinfo->tm_hour, timeinfo->tm_min, timeinfo->tm_sec ); _snprintf(szDumpPath, _MAX_PATH, "%s\\DN\\D\\dumps\\%s", comAppPath, fileName); // create the file HANDLE hFile = ::CreateFile( szDumpPath, GENERIC_WRITE, FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL ); if (hFile!=INVALID_HANDLE_VALUE) { MINIDUMP_CALLBACK_INFORMATION mci; mci.CallbackRoutine = (MINIDUMP_CALLBACK_ROUTINE)MyMiniDumpCallback; mci.CallbackParam = 0; MINIDUMP_TYPE mdt = (MINIDUMP_TYPE)(MiniDumpWithPrivateReadWriteMemory | MiniDumpWithDataSegs | MiniDumpWithHandleData | //MiniDumpWithFullMemoryInfo | //MiniDumpWithThreadInfo | MiniDumpWithProcessThreadData | MiniDumpWithUnloadedModules ); // write the dump BOOL bOK = pDump( process, processId, hFile, mdt, NULL, NULL, &mci ); DWORD lastErr = GetLastError(); if (bOK) { printf("Crash dump saved to: %s\n", szDumpPath); return; } else { _snprintf( szScratch, _MAX_PATH, "Failed to save dump file to '%s' (error %u)", szDumpPath, lastErr); szResult = szScratch; err = ERR_CANTSAVEFILE; } ::CloseHandle(hFile); } else { _snprintf( szScratch, _MAX_PATH, "Failed to create dump file '%s' (error %u)", szDumpPath, GetLastError()); szResult = szScratch; err = ERR_CANTMAKEFILE; } } else { szResult = "DBGHELP.DLL too old"; err = ERR_DBGHELP_TOOLD; } } else { szResult = "DBGHELP.DLL not found"; err = ERR_DBGHELP_NOTFOUND; } printf("Could not produce a crash dump of %s.\n\n[error: %u %s].\n", exe, err, szResult); return; } this code works 100% when its internal to the process (i.e. with SetUnhandledExceptionFilter)

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• Print the first line of a file

  - by Pedro

  void cabclh(){ FILE *fp; char *val, aux; int i=0; char *result, cabeca[60]; fp=fopen("trabalho.txt","r"); if(fp==NULL){ printf("Erro ao abrir o ficheiro\n"); return ; } val=(char*)calloc(aux, sizeof(char)); while(fgetc(fp)=='\n'){ fgets(cabeca,60,fp); printf("%s\n",cabeca); } fclose(fp); free(fp); } void infos(){ FILE *fp; char info[100]; fp=fopen("trabalho.txt","r"); if(fp==NULL){ printf("Erro ao abrir o ficheiro\n"); } while(fgetc(fp)=='-'){ fgets(info,100,fp); printf("%s\n",info); } fclose(fp); } At cabclh i want that the program recognize that the first line is header..but this code doesn't print nothing At infos i want that he recognize that every lines that begin with '-' are info...

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• String concatenation within INFORMIX-SQL "Perform" screens.

  - by Frank Developer

  How can I concatenate two char columns within a perform screen? example: table sample col1 char(1), col2 char(1) . . after editadd of sample let label_3 = sample.col1 + sample.col2 .. this didn't work, I even tried using subscripts for the 2 cols but no dice!

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• Initialize byte array from portion of existing byte array c#

  - by volody

  Is there are an easy way to initialize byte array from portion of existing byte array. I C language is possible to use pointer to say like char s[10] = new char[10]; char* b = s + 5; Is it possible to do that in c#, like: byte[] b = new byte[buffersize]; byte* header = b + 5; byte* data = b + 25;

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• function to get the file name of an URL

  - by user262325

  Hello everyone I have some source code to get the file name of an url for example: http://www.google.com/a.pdf I hope to get a.pdf because the way to join 2 NSStrings I can get is 'appendString' which only for adding a string at right side, so I planned to check each char one by one from the right side of string 'http://www.google.com/a.pdf', when it reach at the char '/', stop the checking, return string fdp.a , after that I change fdp.a to a.pdf source codes are below -(NSMutableString *) getSubStringAfterH : originalString:(NSString *)s0 { NSInteger i,l; l=[s0 length]; NSMutableString *h=[[NSMutableString alloc] init]; NSMutableString *ttt=[[NSMutableString alloc] init ]; for(i=l-1;i>=0;i--) //check each char one by one from the right side of string 'http://www.google.com/a.pdf', when it reach at the char '/', stop { ttt=[s0 substringWithRange:NSMakeRange(i, 1)]; if([ttt isEqualToString:@"/"]) { break; } else { [h appendString:ttt]; } } [ttt release]; //below are to change the sequence of char in h // txt.edcba -> abcde.txt NSMutableString *h1=[[[NSMutableString alloc] initWithFormat:@""] autorelease]; for (i=[h length]-1;i>=0;i--) { NSMutableString *t1=[[NSMutableString alloc] init ]; t1=[h substringWithRange:NSMakeRange(i, 1)]; [h1 appendString:t1]; [t1 release]; } [h release]; return h1; } h1 can reuturn the coorect string a.pdf, but if it returns to the codes where it was called, after a while system reports 'double free * set a breakpoint in malloc_error_break to debug' I checked a long time and foudn that if I removed the code ttt=[s0 substringWithRange:NSMakeRange(i, 1)]; everything will be Ok (of course getSubStringAfterH can not returns the corrent result I expected.), no error reported. I try to fix the bug a few hours, but still no clue. Welcome any comment Thanks interdev

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• Union struct produces garbage and general question about struct nomenclature

  - by SoulBeaver

  I read about unions the other day( today ) and tried the sample functions that came with them. Easy enough, but the result was clear and utter garbage. The first example is: union Test { int Int; struct { char byte1; char byte2; char byte3; char byte4; } Bytes; }; where an int is assumed to have 32 bits. After I set a value Test t; t.Int = 7; and then cout cout << t.Bytes.byte1 << etc... the individual bytes, there is nothing displayed, but my computer beeps. Which is fairly odd I guess. The second example gave me even worse results. union SwitchEndian { unsigned short word; struct { unsigned char hi; unsigned char lo; } data; } Switcher; Looks a little wonky in my opinion. Anyway, from the description it says, this should automatically store the result in a high/little endian format when I set the value like Switcher.word = 7656; and calling with cout << Switcher.data.hi << endl The result of this were symbols not even defined in the ASCII chart. Not sure why those are showing up. Finally, I had an error when I tried correcting the example by, instead of placing Bytes at the end of the struct, positioning it right next to it. So instead of struct {} Bytes; I wanted to write struct Bytes {}; This tossed me a big ol' error. What's the difference between these? Since C++ cannot have unnamed structs it seemed, at the time, pretty obvious that the Bytes positioned at the beginning and at the end are the things that name it. Except no, that's not the entire answer I guess. What is it then?

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• SIMPLE OpenSSL RSA Encryption in C/C++ is causing me headaches

  - by Josh

  Hey guys, I'm having some trouble figuring out how to do this. Basically I just want a client and server to be able to send each other encrypted messages. This is going to be incredibly insecure because I'm trying to figure this all out so I might as well start at the ground floor. So far I've got all the keys working but encryption/decryption is giving me hell. I'll start by saying I am using C++ but most of these functions require C strings so whatever I'm doing may be causing problems. Note that on the client side I receive the following error in regards to decryption. error:04065072:rsa routines:RSA_EAY_PRIVATE_DECRYPT:padding check failed I don't really understand how padding works so I don't know how to fix it. Anywho here are the relevant variables on each side followed by the code. Client: RSA *myKey; // Loaded with private key // The below will hold the decrypted message unsigned char* decrypted = (unsigned char*) malloc(RSA_size(myKey)); /* The below holds the encrypted string received over the network. Originally held in a C-string but C strings never work for me and scare me so I put it in a C++ string */ string encrypted; // The reinterpret_cast line was to get rid of an error message. // Maybe the cause of one of my problems? if(RSA_private_decrypt(sizeof(encrypted.c_str()), reinterpret_cast<const unsigned char*>(encrypted.c_str()), decrypted, myKey, RSA_PKCS1_OAEP_PADDING)==-1) { cout << "Private decryption failed" << endl; ERR_error_string(ERR_peek_last_error(), errBuf); printf("Error: %s\n", errBuf); free(decrypted); exit(1); } Server: RSA *pkey; // Holds the client's public key string key; // Holds a session key I want to encrypt and send //The below will hold the encrypted message unsigned char *encrypted = (unsigned char*)malloc(RSA_size(pkey)); // The reinterpret_cast line was to get rid of an error message. // Maybe the cause of one of my problems? if(RSA_public_encrypt(sizeof(key.c_str()), reinterpret_cast<const unsigned char*>(key.c_str()), encrypted, pkey, RSA_PKCS1_OAEP_PADDING)==-1) { cout << "Public encryption failed" << endl; ERR_error_string(ERR_peek_last_error(), errBuf); printf("Error: %s\n", errBuf); free(encrypted); exit(1); } Let me once again state, in case I didn't before, that I know my code sucks but I'm just trying to establish a framework for understanding this. I'm sorry if this offends you veteran coders. Thanks in advance for any help you guys can provide!

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• Initialize byte array from a portion of existing byte array c#

  - by volody

  Is there are an easy way to initialize byte array from portion of existing byte array. In C language it is possible to use pointer to say like char s[10] = new char[10]; char* b = s + 5; Is it possible to do that in c#, like: byte[] b = new byte[buffersize]; byte* header = b + 5; byte* data = b + 25;

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• Need help with basic ASM

  - by Malfist

  Hello, I'm trying to convert some c code to assmebly, and I need some help. char encode(char plain){ __asm{ mov eax, plain add eax, 2 ret } //C code /* char code; code = plain+2; return code;*/ } First problem is that visual studio complains that the register size doesn't match, i.e. eax is too small/large for char. I was under the impression that they were both DWORDs. Also, if I leave the variable in eax, and ret in assembly, it'll actually return that variable, right?

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• Best way to create SEO friendly URI string

  - by Mat Banik

  The method below allows only "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-" chars in URI strings. What better way is there to make nice SEO URI string? import org.apache.commons.lang.StringUtils; public static String safeChar(String input) { input = input.trim(); input = StringUtils.replace(input, " -", "-"); input = StringUtils.replace(input, "- ", "-"); input = StringUtils.replace(input, " - ", "-"); input = StringUtils.replaceChars(input, '\'', '-'); input = StringUtils.replaceChars(input, ' ', '-'); char[] allowed = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-".toCharArray(); char[] charArray = input.toCharArray(); StringBuilder result = new StringBuilder(); for (char c : charArray) { for (char a : allowed) { if (c == a) result.append(a); } } return result.toString(); }

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