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• Accessing structure elements using pointers

  - by Arun Nadesh

  Hi Everybody, Greetings! I got surprised when the following program did not crash. typedef struct _x{ int a; char b; int c; }x; main() { x *ptr=0; char *d=&ptr->b; } As per my understanding the -> operator has higher precedence over & operator. So I expected the program to crash at the below statement when we try to dereference the NULL pointer tr. char *d=&ptr->b; But the statement &ptr->b evaluates to a valid address. Could somebody please explain where I'm wrong? Thanks & Regards, Arun

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• C++ porting templates to Red hat enterprise linux version 5

  - by mkal

  #include <sys/stat.h> #include <sys/types.h> #include <unistd.h> template <class OutType> bool getVAL(OutType &value_out, const std::string &key) { return false; } int main (int argc, char*argv[]) { mode_t a; getVAL(a, "abc"); } test.cpp:6: error: ISO C++ forbids declaration of ‘parameter’ with no type test.cpp: In function ‘int main(int, char**)’: test.cpp:13: error: no matching function for call to ‘getVAL(mode_t&, const char [4])’

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• Using an array in embedded x86 assembly??

  - by Mark V.

  Hey all I have a method (C++) that returns a character and takes an array of characters as its parameters. I'm messing with assembly for the first time and just trying to return the first character of the array in the dl register. Here's what I have so far: char returnFirstChar(char arrayOfLetters[]) { char max; __asm { push eax push ebx push ecx push edx mov dl, 0 mov eax, arrayOfLetters[0] xor edx, edx mov dl, al mov max, dl pop edx pop ecx pop ebx pop eax } return max; } For some reason this method returns a ? Any idea whats going on? Thanks

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• How to pass the structure to a function in C++ defined in another class?

  - by Dany

  I have a class Con as this:- class Con { public: struct MachineList { BSTR AccountId; BSTR MachineId; BSTR Make; char* Make1; BSTR Model; char* Model1; BSTR SerialNumber; BSTR IpAddress; char* IpAddress1; BSTR Port; int Port1; BSTR LocationCode; } machinelist[100] ; int w; } ; i created an object of Con class as Con m_con; I have another class Test class Test { public: void fun();//i want to pass the object of the structure that i created in Con //what arguments should i pass in fun function? };

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• Embedding binary blobs using gcc mingw

  - by myforwik

  I am trying to embed binary blobs into an exe file. I am using mingw gcc. I make the object file like this: ld -r -b binary -o binary.o input.txt I then look objdump output to get the symbols: objdump -x binary.o And it gives symbols named: _binary_input_txt_start _binary_input_txt_end _binary_input_txt_size I then try and access them in my C program: #include <stdlib.h> #include <stdio.h> extern char _binary_input_txt_start[]; int main (int argc, char *argv[]) { char *p; p = _binary_input_txt_start; return 0; } Then I compile like this: gcc -o test.exe test.c binary.o But I always get: undefined reference to _binary_input_txt_start Does anyone know what I am doing wrong?

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• inserting std::strings in to a std::map

  - by PaulH

  I have a program that reads data from a file line-by-line. I would like to copy some substring of that line in to a map as below: std::map< DWORD, std::string > my_map; DWORD index; // populated with some data char buffer[ 1024 ]; // populated with some data char* element_begin; // points to some location in buffer char* element_end; // points to some location in buffer > element_begin my_map.insert( std::make_pair( index, std::string( element_begin, element_end ) ) ); This std::map<>::insert() operation takes a long time (It doubles the file parsing time). Is there a way to make this a less expensive operation? Thanks, PaulH

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• realloc()ing memory for a buffer used in recv()

  - by Hristo

  I need to recv() data from a socket and store it into a buffer, but I need to make sure get all of the data so I have things in a loop. So to makes sure I don't run out of room in my buffer, I'm trying to use realloc to resize the memory allocated to the buffer. So far I have: // receive response int i = 0; int amntRecvd = 0; char *pageContentBuffer = (char*) malloc(4096 * sizeof(char)); while ((amntRecvd = recv(proxySocketFD, pageContentBuffer + i, 4096, 0)) > 0) { i += amntRecvd; realloc(pageContentBuffer, 4096 + sizeof(pageContentBuffer)); } However, this doesn't seem to be working properly since Valgrind is complaining "valgrind: the 'impossible' happened:". Any advice as to how this should be done properly? Thanks, Hristo

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• Does printf have side effects?

  - by martani_net

  I have an array of the following strcuture struct T_info { char capitale[255]; char pays[255]; char commentaire[255]; }; struct T_info *tableau; Then when I populate the array and call printf allone on each element it works fine strcpy(tab[line].capitale, buffer); strcpy(tab[line].pays, buffer); strcpy(tab[line].commentaire, buffer); printf("%s\n", tab[line].capitale); printf("%s\n", tab[line].pays); printf("%s\n", tab[line].commentaire); but if I call, printf("%s, %s, %s", tab[line].capitale, tab[line].pays, tab[line].commentaires) I get wrong resutts, is printf changing its parameters or what is going on?

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• anagram!! problem with this code

  - by danielDhobbs

  hello people!! i have a problem with this code can you fix it for me? int anagram(char* word, int cur, int len){ int i, b = cur+1; char temp=0; char arrA[len]; printf("//%d**%d//", b, cur); for (i = 0 ; i < len ; i++) { arrA[i] = word[i]; } for (i = cur ; i < len ; i++) { if (b < len) { printf("%s\n", arrA); temp = arrA[cur]; arrA[cur] = arrA[b]; arrA[b] = temp; b++; } else if (b == len) anagram(arrA, b, len); } return 0; }

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• How to convert a unicode charactor array back to unicode sequence in C++

  - by eddyxd

  My problem is how to convert a c/c++ string/chractor array to another string contain the unicode(UTF-16) escape sequence of original one for example, I want to find a function F(char *ch) could do following function. char a[10] = "\u5f53"; printf("a = %s\n",a); char b[10]; b = F(a); //<- F is the function I wanted printf("b = %s\n",b); -------- console will show ------- a = ? b = \u5f53 Anyone has any Idea@@?~ thanks!! ps: I tried to guess \u5f35 means the value store in a, but it is not indeed the value of a[0] = -79 , a[1] = 105 ... So I don't know how to convert it back to the sequence of unicode.... Please give me a hane~ : )

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• Function Pointer from base class

  - by camelord

  Hi there, i need a Function Pointer from a base class. Here is the code: class CActionObjectBase { ... void AddResultStateErrorMessage( const char* pcMessage , ULONG iResultStateCode); ... } CActionObjectCalibration( ): CActionObjectBase() { ... m_Calibration = new CCalibration(&CActionObjectBase::AddResultStateErrorMessage); } class CCalibration { ... CCalibration(void (CActionObjectBase::* AddErrorMessage)(const char*, ULONG )); ... void (CActionObjectBase::* m_AddErrorMessage)(const char*, ULONG ); } Inside CCalibration in a Function occurs the Error. I try to call the Function Pointer like this: if(m_AddErrorMessage) { ... m_AddErrorMessage("bla bla", RSC_FILE_ERROR); } The Problem is, that I cannot compile. The Error Message says something like: error C2064: Expression is no Function, that takes two Arguments. What is wrong? regards camelord

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• Why isn't wchar_t widely used in code for Linux / related platforms?

  - by Ninefingers

  This intrigues me, so I'm going to ask - for what reason is wchar_t not used so widely on Linux/Linux-like systems as it is on Windows? Specifically, the Windows API uses wchar_t internally whereas I believe Linux does not and this is reflected in a number of open source packages using char types. My understanding is that given a character c which requires multiple bytes to represent it, then in a char[] form c is split over several parts of char* whereas it forms a single unit in wchar_t[]. Is it not easier, then, to use wchar_t always? Have I missed a technical reason that negates this difference? Or is it just an adoption problem?

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• Copy constructor demo (crashing... case 2)

  - by AKN

  Please have a glance at this program: class CopyCon { public: char *name; CopyCon() { name = new char[20]; name = "Hai";//_tcscpy(name,"Hai"); } CopyCon(const CopyCon &objCopyCon) { name = new char[_tcslen(objCopyCon.name)+1]; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete[] name; name = NULL; } } }; int main() { CopyCon obj1; CopyCon obj2(obj1); cout<<obj1.name<<endl; cout<<obj2.name<<endl; } This program crashes on execution. Error: "Expression: _BLOCK_TYPE_IS_VALID(pHead-nBlockUse)" If I assign "Hai" to name using aasignment operator, its crashing. Where as when I use string func _tcscpy to assign "Hai" to name, its working perfectly. Can some one explain why so?

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• A question for retrieve minix os version

  - by majnun

  Hi guys i'm having a project for the university in which (above others ) i have to get the minix os version from kernell call.I'm not a very experienced programmer so this is what i have come to (with some help ) int main (int argc, char *argv[] ) { char M3ca1[23]; message ml; m.m_u.m_m1.m3ca1= OS_VERSION; char temp=_syscall(MM,69,&m); printf("the os version is %c\n",temp); return 0; } and i get multiple errors.IF you have any ideas it would be greatly appreciated.

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• DB2 ZOS String Comparison Problem

  - by John

  I am comparing some CHAR data in a where clause in my sql like this, where PRI_CODE < PriCode The problem I am having is when the CHAR values are of different lengths. So if PRI_CODE = '0800' and PriCode = '20' it is returning true instead of false. It looks like it is comparing it like this '08' < '20' instead of like '0800' < '20' Does a CHAR comparison start from the Left until one or the other values end? If so how do I fix this? My values can have letters in it so convering to numeric is not an option.

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• Trying to understand strtok

  - by Karthick

  Consider the following snippet that uses strtok to split the string madddy. char* str = (char*) malloc(sizeof("Madddy")); strcpy(str,"Madddy"); char* tmp = strtok(str,"d"); std::cout<<tmp; do { std::cout<<tmp; tmp=strtok(NULL, "dddy"); }while(tmp!=NULL); It works fine, the output is Ma. But by modifying the strtok to the following, tmp=strtok(NULL, "ay"); The output becomes Madd. So how does strtok exactly work? I have this question because I expected strtok to take each and every character that is in the delimiter string to be taken as a delimiter. But in certain cases it is doing that way but in few cases, it is giving unexpected results. Could anyone help me understand this?

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• C#: What is the preferred way to handle this error?

  - by Ash

  I have a class 'Hand' that consists of two playing cards as below: public class Card { public char r, s; public Card(char rank, char suit) { r = rank; s = suit; } } public class Hand { public Card c1, c2; public Hand(Card one, Card two) { c1 = one; c2 = two; } } In a 52 card deck we can't have two identical cards. How should I deal with an error where I accidentally instance a class with two identical cards, e.g (Ah, Ah)? Thanks, Ash

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• is my function correct?

  - by sbsp

  This is part of an assignment so please dont post solutions, just point me in the right direction if possible? I am passing a pointer to a char array to my method, as well as a value for the actual height of the char array. I am looping through to see if all values are 0, if they are then return 0, esle return one The method is used as a test to see if i should free memory or not and set the pointer to null if it is full of 0's. The issue i am having is that the programme should have "some unfree" memory at the end, so i have no idea whether or not its doing it correctly - and gdb i struggle with immensley. Thanks for reading int shouldBeNull(char *charPointer, int sizeOfCharArray) { int isIn = 0; int i = 0; while(i < sizeOfCharArray){ if(*charPointer != '0'){ isIn = 1; break; } i++; charPointer++; } return isIn; }

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• NSBitmapImageRep data Format as application icon image??

  - by Joe

  i have a char* array of data that was in RGBA and then moved to ARGB Bottom line is the set application image looks totally messed up and i cant put my finger on why? //create a bitmap representation of the image data. //The data is expected to be unsigned char** NSBitmapImageRep *bitmap = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes : (unsigned char**) &dest pixelsWide:width pixelsHigh:height bitsPerSample:8 samplesPerPixel:4 hasAlpha:YES isPlanar:NO colorSpaceName:NSDeviceRGBColorSpace bitmapFormat:NSAlphaFirstBitmapFormat bytesPerRow: 0 bitsPerPixel:0 ]; NSImage *image = [[NSImage alloc] initWithSize:NSMakeSize(width, height)]; [image addRepresentation:bitmap]; if( image == NULL) { printf("image is null\n"); fflush(stdout); } [NSApp setApplicationIconImage :image]; What in these values is off? the image looks very multicolored and pixelated, with transparent parts/lines as well.

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• Variadic functions and arguments assignment in C/C++

  - by Rizo

  I was wondering if in C/C++ language it is possible to pass arguments to function in key-value form. For example in python you can do: def some_function(arg0 = "default_value", arg1): # (...) value1 = "passed_value" some_function(arg1 = value1) So the alternative code in C could look like this: void some_function(char *arg0 = "default_value", char *arg1) { ; } int main() { char *value1 = "passed_value"; some_function(arg1 = value1); return(0); } So the arguments to use in some_function would be: arg0 = "default_value" arg1 = "passed_value" Any ideas?

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• why does this code crash?

  - by ashish yadav

  why does this code crash? is using strcat illegal on character pointers? #include <stdio.h> #include <string.h> int main() { char *s1 = "Hello, "; char *s2 = "world!"; char *s3 = strcat(s1, s2); printf("%s",s3); return 0; } please give a proper way with referring to both array and pointers.

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• Why does this code read all ' ' for the anything after the 4th character?

  - by djs22

  #define fileSize 100000 int main(int argc, char *argv[]){ char *name=argv[1]; char ret[fileSize]; FILE *fl = fopen(name, "rb"); fseek(fl, 0, SEEK_END); long len = fileSize; fseek(fl, 0, SEEK_SET); //fread(ret, 1, len, fl); int i; *(ret+fileSize) = '\0'; for (i=0; i<fileSize; i++){ *(ret+i)=fgetc(fl); printf("byte : %s \n", ret); } fclose(fl); } In the above code, when I feed the name of a jpeg file, it reads anything after the 4th character as ' '...any ideas? Thanks!

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• Class members allocation on heap/stack? C++

  - by simplebutperfect

  If a class is declared as follows: class MyClass { char * MyMember; MyClass() { MyMember = new char[250]; } ~MyClass() { delete[] MyMember; } }; And it could be done like this: class MyClass { char MyMember[250]; }; How does a class gets allocated on heap, like if i do MyClass * Mine = new MyClass(); Does the allocated memory also allocates the 250 bytes in the second example along with the class instantiation? And will the member be valid for the whole lifetime of MyClass object? As for the first example, is it practical to allocate class members on heap?

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• "Data type mismatch in criteria expression"

  - by simon

  Hey guys ! I have a problem when i want to insert values from textboxes to my access database ! When i want to save i get that error ("Data type mismatch in criteria expression") The code: string conString = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=C:\Users\Simon\Desktop\test5\test5\test5\save.mdb"; OleDbConnection empConnection = new OleDbConnection(conString); string insertStatement = "INSERT INTO aktivnosti_save " + "([ID_uporabnika],[ID_aktivnosti],[kalorij]) " + "VALUES (@ID_uporabnika,@ID_aktivnosti,@kalorij)"; OleDbCommand insertCommand = new OleDbCommand(insertStatement, empConnection); insertCommand.Parameters.Add("@ID_uporabnika", OleDbType.Char).Value = textBox3.Text; insertCommand.Parameters.Add("@ID_zivila", OleDbType.Char).Value = iDTextBox.Text; insertCommand.Parameters.Add("@kalorij", OleDbType.Char).Value = textBox2.Text; empConnection.Open(); try { int count = insertCommand.ExecuteNonQuery(); } catch (OleDbException ex) { MessageBox.Show(ex.Message); } finally { empConnection.Close(); textBox1.Clear(); textBox2.Clear(); } }

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• Data Types and Structs

  - by dubya

  I'm reviewing for a test, and I am stumped by this question. Consider the following declarations: enum CategoryType {HUMANITIES, SOCIALSCIENCE, NATURALSCIENCE}; const int NUMCOURSES = 100; struct CourseRec { string courseName; int courseNum; CategoryType courseCategory; }; typedef CourseRec CourseList [NUMCOURSES]; CourseList courses; int index1, index2; What is the data type of the expression courses[index1] .courseName[index2] ? (a) CourseList (b) CourseRec (c) string (d) char (e) none; the expression is syntactically invalid I thought that the answer would be string, since courseName is a string, or maybe even CourseRec, since it is in the struct, but the answer is (d)char. Why is this a char data type? Any help is greatly appreciated.

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