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• Trouble with Unions in C program.

  - by Jordan S

  I am working on a C program that uses a Union. The union definition is in FILE_A header file and looks like this... // FILE_A.h**************************************************** xdata union { long position; char bytes[4]; }CurrentPosition; If I set the value of CurrentPosition.position in FILE_A.c and then call a function in FILE_B.c that uses the union, the data in the union is back to Zero. This is demonstrated below. // FILE_A.c**************************************************** int main.c(void) { CurrentPosition.position = 12345; SomeFunctionInFileB(); } // FILE_B.c**************************************************** void SomeFunctionInFileB(void) { // After the following lines execute I see all zeros in the flash memory. WriteByteToFlash(CurrentPosition.bytes[0]; WriteByteToFlash(CurrentPosition.bytes[1]; WriteByteToFlash(CurrentPosition.bytes[2]; WriteByteToFlash(CurrentPosition.bytes[3]; } Now, If I pass a long to SomeFunctionInFileB(long temp) and then store it into CurrentPosition.bytes within that function, and finally call WriteBytesToFlash(CurrentPosition.bytes[n]... it works just fine. It appears as though the CurrentPosition Union is not global. So I tried changing the union definition in the header file to include the extern keyword like this... extern xdata union { long position; char bytes[4]; }CurrentPosition; and then putting this in the source (.c) file... xdata union { long position; char bytes[4]; }CurrentPosition; but this causes a compile error that says: C:\SiLabs\Optec Programs\AgosRot\MotionControl.c:76: error 91: extern definition for 'CurrentPosition' mismatches with declaration. C:\SiLabs\Optec Programs\AgosRot\/MotionControl.h:48: error 177: previously defined here So what am I doing wrong? How do I make the union global?

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• Can someone explain me this code ?

  - by VaioIsBorn

  #include <stdio.h> #include <unistd.h> #include <string.h> int good(int addr) { printf("Address of hmm: %p\n", addr); } int hmm() { printf("Win.\n"); execl("/bin/sh", "sh", NULL); } extern char **environ; int main(int argc, char **argv) { int i, limit; for(i = 0; environ[i] != NULL; i++) memset(environ[i], 0x00, strlen(environ[i])); int (*fptr)(int) = good; char buf[32]; if(strlen(argv[1]) <= 40) limit = strlen(argv[1]); for(i = 0; i <= limit; i++) { buf[i] = argv[1][i]; if(i < 36) buf[i] = 0x41; } int (*hmmptr)(int) = hmm; (*fptr)((int)hmmptr); return 0; } I don't really understand the code above, i have it from an online game - i should supply something in the arguments so it would give me shell, but i don't get it how it works so i don't know what to do. So i need someone that would explain it what it does, how it's working and the stuff. Thanks.

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• Android - Read PNG image without alpha and decode as ARGB_8888

  - by loki666

  I try to read an image from sdcard (in emulator) and then create a Bitmap image with the BitmapFactory.decodeByteArray method. I set the options: options.inPrefferedConfig = Bitmap.Config.ARGB_8888 options.inDither = false Then I extract the pixels into a ByteBuffer. ByteBuffer buffer = ByteBuffer.allocateDirect(width*height*4) bitmap.copyPixelsToBuffer(buffer) I use this ByteBuffer then in the JNI to convert it into RGB format and want to calculate on it. But always I get false data - I test without modifying the ByteBuffer. Only thing I do is to put it into the native method into JNI. Then cast it into a unsigned char* and convert it back into a ByteBuffer before returning it back to Java. unsigned char* buffer = (unsinged char*)(env->GetDirectBufferAddress(byteBuffer)) jobject returnByteBuffer = env->NewDirectByteBuffer(buffer, length) Before displaying the image I get data back with bitmap.copyPixelsFromBuffer( buffer ) But then it has wrong data in it. My Question is if this is because the image is internally converted into RGB 565 or what is wrong here? ..... Have an answer for it: - yes, it is converted internally to RGB565. Does anybody know how to create such an bitmap image from PNG with ARGB8888 pixel format? If anybody has an idea, it would be great!

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• Deleting a node from linked list in C

  - by LuckySlevin

  My problem is deleting a node from linked list. I have two structs : typedef struct inner_list { int count; char word[100]; inner_list*next; } inner_list; typedef struct outer_list { char word [100]; inner_list * head; int count; outer_list * next; } outer_list; My problem is in deleting a node from outer_list linked list. For example when user entered aaa to delete, delete function should find the node with outer_list->word = aaa and delete this node and reconnect the list again. I tried the below code to do this. but After finding and deleting I'm losing the list. I don't know what's wrong. Please notice that outer_list have also a linked list of inner_list inside. void delnode(outer_list *head,char num[100]) { outer_list *temp, *m; temp=head; while(temp!=NULL) { if(strcmp(temp->word==num)==0) { if(temp==head) { head=temp->next; free(temp); return; } else { m->next=temp->next; free(temp); return; } }else { m=temp; temp= temp->next; } } printf(" ELEMENT %s NOT FOUND ", num); } What are your ideas about this?

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• C++ Beginner Delete Question

  - by Pooch

  Hi all, This is my first year learning C++ so bear with me. I am attempting to dynamically allocate memory to the heap and then delete the allocated memory. Below is the code that is giving me a hard time: // String.cpp #include "String.h" String::String() {} String::String(char* source) { this->Size = this->GetSize(source); this->CharArray = new char[this->Size + 1]; int i = 0; for (; i < this->Size; i++) this->CharArray[i] = source[i]; this->CharArray[i] = '\0'; } int String::GetSize(const char * source) { int i = 0; for (; source[i] != '\0'; i++); return i; } String::~String() { delete[] this->CharArray; } Here is the error I get when the compiler tries to delete the CharArray: 0xC0000005: Access violation reading location 0xccccccc0. And here is the last call on the stack: msvcr100d.dll!operator delete(void * pUserData) Line 52 + 0x3 bytes C++ I am fairly certain the error exists within this piece of code but will provide you with any other information needed. Oh yeah, using VS 2010 for XP. Thanks for any and all help!

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• Unhandled Exception error message

  - by Joshua Green

  Does anyone know why including a term such as: t = PL_new_term_ref(); would cause an Unhandled Exception error message: 0xC0000005: Access violation reading location 0x0000000c. (Visual Studio 2008) I have a header file: class UserTaskProlog : public ArAction { public: UserTaskProlog( const char* name = " sth " ); ~UserTaskProlog( ); AREXPORT virtual ArActionDesired *fire( ArActionDesired currentDesired ); private: term_t t; }; and a cpp file: UserTaskProlog::UserTaskProlog( const char* name ) : ArAction( name, " sth " ) { char** argv; argv[ 0 ] = "libpl.dll"; PL_initialise( 1, argv ); PlCall( "consult( 'myProg.pl' )" ); } UserTaskProlog::~UserTaskProlog( ) { } ArActionDesired *UserTaskProlog::fire( ArActionDesired currentDesired ) { cout << " something " << endl; t = PL_new_term_ref( ); } Without t=PL_new_term_ref() everything works fine, but when I start adding my Prolog code (declarations first, such as t=PL_new_term_ref), I get this Access Violation error message. I'd appreciate any help. Thanks,

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• C++ Check Substring of a String

  - by user69514

  I'm trying to check whether or not the second argument in my program is a substring of the first argument. The problem is that it only work if the substring starts with the same letter of the string. .i.e Michigan - Mich (this works) Michigan - Mi (this works) Michigan - igan (this doesn't work) #include <stdio.h> #include <string.h> #include <string> using namespace std; bool my_strstr( string str, string sub ) { bool flag = true; int startPosition = -1; char subStart = str.at(0); char strStart; //find starting position for(int i=0; i<str.length(); i++){ if(str.at(i) == subStart){ startPosition = i; break; } } for(int i=0; i<sub.size(); i++){ if(sub.at(i) != str.at(startPosition)){ flag = false; break; } startPosition++; } return flag; } int main(int argc, char **argv){ if (argc != 3) { printf ("Usage: check <string one> <string two>\n"); } string str1 = argv[1]; string str2 = argv[2]; bool result = my_strstr(str1, str2); if(result == 1){ printf("%s is a substring of %s\n", argv[2], argv[1]); } else{ printf("%s is not a substring of %s\n", argv[2], argv[1]); } return 0; }

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• How do I optimize this postfix expression tree for speed?

  - by Peter Stewart

  Thanks to the help I received in this post: I have a nice, concise recursive function to traverse a tree in postfix order: deque <char*> d; void Node::postfix() { if (left != __nullptr) { left->postfix(); } if (right != __nullptr) { right->postfix(); } d.push_front(cargo); return; }; This is an expression tree. The branch nodes are operators randomly selected from an array, and the leaf nodes are values or the variable 'x', also randomly selected from an array. char *values[10]={"1.0","2.0","3.0","4.0","5.0","6.0","7.0","8.0","9.0","x"}; char *ops[4]={"+","-","*","/"}; As this will be called billions of times during a run of the genetic algorithm of which it is a part, I'd like to optimize it for speed. I have a number of questions on this topic which I will ask in separate postings. The first is: how can I get access to each 'cargo' as it is found. That is: instead of pushing 'cargo' onto a deque, and then processing the deque to get the value, I'd like to start processing it right away. I don't yet know about parallel processing in c++, but this would ideally be done concurrently on two different processors. In python, I'd make the function a generator and access succeeding 'cargo's using .next(). But I'm using c++ to speed up the python implementation. I'm thinking that this kind of tree has been around for a long time, and somebody has probably optimized it already. Any Ideas? Thanks

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• Accessing memory buffer after fread()

  - by xiongtx

  I'm confused as to how fread() is used. Below is an example from cplusplus.com /* fread example: read a complete file */ #include <stdio.h> #include <stdlib.h> int main () { FILE * pFile; long lSize; char * buffer; size_t result; pFile = fopen ( "myfile.bin" , "rb" ); if (pFile==NULL) {fputs ("File error",stderr); exit (1);} // obtain file size: fseek (pFile , 0 , SEEK_END); lSize = ftell (pFile); rewind (pFile); // allocate memory to contain the whole file: buffer = (char*) malloc (sizeof(char)*lSize); if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);} // copy the file into the buffer: result = fread (buffer,1,lSize,pFile); if (result != lSize) {fputs ("Reading error",stderr); exit (3);} /* the whole file is now loaded in the memory buffer. */ // terminate fclose (pFile); free (buffer); return 0; } Let's say that I don't use fclose() just yet. Can I now just treat buffer as an array and access elements like buffer[i]? Or do I have to do something else?

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• Sending buffered images between Java client and Twisted Python socket server

  - by PattimusPrime

  I have a server-side function that draws an image with the Python Imaging Library. The Java client requests an image, which is returned via socket and converted to a BufferedImage. I prefix the data with the size of the image to be sent, followed by a CR. I then read this number of bytes from the socket input stream and attempt to use ImageIO to convert to a BufferedImage. In abbreviated code for the client: public String writeAndReadSocket(String request) { // Write text to the socket BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); bufferedWriter.write(request); bufferedWriter.flush(); // Read text from the socket BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream())); // Read the prefixed size int size = Integer.parseInt(bufferedReader.readLine()); // Get that many bytes from the stream char[] buf = new char[size]; bufferedReader.read(buf, 0, size); return new String(buf); } public BufferedImage stringToBufferedImage(String imageBytes) { return ImageIO.read(new ByteArrayInputStream(s.getBytes())); } and the server: # Twisted server code here # The analog of the following method is called with the proper client # request and the result is written to the socket. def worker_thread(): img = draw_function() buf = StringIO.StringIO() img.save(buf, format="PNG") img_string = buf.getvalue() return "%i\r%s" % (sys.getsizeof(img_string), img_string) This works for sending and receiving Strings, but image conversion (usually) fails. I'm trying to understand why the images are not being read properly. My best guess is that the client is not reading the proper number of bytes, but I honestly don't know why that would be the case. Side notes: I realize that the char[]-to-String-to-bytes-to-BufferedImage Java logic is roundabout, but reading the bytestream directly produces the same errors. I have a version of this working where the client socket isn't persistent, ie. the request is processed and the connection is dropped. That version works fine, as I don't need to care about the image size, but I want to learn why the proposed approach doesn't work.

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• C Programing - Return libcurl http response to string to the calling function

  - by empty set

  I have a homework and i need somehow to compare two http responses. I am writing it on C (dumb decision) and i use libcurl to make things easier. I am calling the function that uses libcurl to http request and response from another function and i want to return the http response to it. Anyway, the code below doesn't work, any ideas? #include <stdio.h> #include <curl/curl.h> #include <string.h> size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream) { size_t written; written = fwrite(ptr, size, nmemb, stream); return written; } char *handle_url(void) { CURL *curl; char *fp; CURLcode res; char *url = "http://www.yahoo.com"; curl = curl_easy_init(); if (curl) { curl_easy_setopt(curl, CURLOPT_URL, url); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data); curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp); res = curl_easy_perform(curl); if(res != CURLE_OK) fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res)); curl_easy_cleanup(curl); //printf("\n%s", fp); } return fp; } This solution C libcurl get output into a string works, but not in my case because i want to return this string to the calling function.

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• How to easily map c++ enums to strings

  - by Roddy

  I have a bunch of enum types in some library header files that I'm using, and I want to have a way of converting enum values to user strings - and vice-versa. RTTI won't do it for me, because the 'user strings' need to be a bit more readable than the enumerations. A brute force solution would be a bunch of functions like this, but I feel that's a bit too C-like. enum MyEnum {VAL1, VAL2,VAL3}; String getStringFromEnum(MyEnum e) { switch e { case VAL1: return "Value 1"; case VAL2: return "Value 2"; case VAL1: return "Value 3"; default: throw Exception("Bad MyEnum"); } } I have a gut feeling that there's an elegant solution using templates, but I can't quite get my head round it yet. UPDATE: Thanks for suggestions - I should have made clear that the enums are defined in a third-party library header, so I don't want to have to change the definition of them. My gut feeling now is to avoid templates and do something like this: char * MyGetValue(int v, char *tmp); // implementation is trivial #define ENUM_MAP(type, strings) char * getStringValue(const type &T) \ { \ return MyGetValue((int)T, strings); \ } ; enum eee {AA,BB,CC}; - exists in library header file ; enum fff {DD,GG,HH}; ENUM_MAP(eee,"AA|BB|CC") ENUM_MAP(fff,"DD|GG|HH") // To use... eee e; fff f; std::cout<< getStringValue(e); std::cout<< getStringValue(f);

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• Passing parameter to pthread

  - by Andrei Ciobanu

  Hello, i have the following code: #include <stdlib.h> #include <stdio.h> #include <pthread.h> #define NUM_THREADS 100 struct thread_param { char *f1; char *f2; int x; }; void *thread_function(void *arg){ printf("%d\n", ((struct thread_param*)arg)->x); } int main(int argc, char *argvs[]){ int i, thread_cr_res = 0; pthread_t *threads; threads = malloc(100 * sizeof(*threads)); if(threads == NULL){ fprintf(stderr,"MALLOC THREADS ERROR"); return (-1); } for(i = 0; i < NUM_THREADS; i++){ struct thread_param *tp; if((tp = malloc(sizeof(*tp))) == NULL){ fprintf(stderr,"MALLOC THREAD_PARAM ERROR"); return (-1); } tp->f1 = "f1"; tp->f2 = "f2"; tp->x = i; thread_cr_res = pthread_create(&threads[i], NULL, thread_function, (void*)tp); if(thread_cr_res != 0){ fprintf(stderr,"THREAD CREATE ERROR"); return (-1); } } return (0); } What i want to achieve, is to print all the numbers from 0 to 99, from threads. Also i am experimenting a way to pass a structure as a thread input parameter. What i am finding curios, is that not all the numbers are shown, eg: ./a.out | grep 9 9 19 29 39 49 And sometimes some numbers are shown twice: ... 75 74 89 77 78 79 91 91 Can you please explain me why is this happening ? No errors are shown.

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• Having some fun - what is a good way to include a secret key functionality and fire the KeyDown event?

  - by Sisyphus

  To keep myself interested, I try to put little Easter Eggs in my projects (mostly to amuse myself). I've seen some websites where you can type a series of letters "aswzaswz" and you get a "secret function" - how would I achieve this in C#? I've assigned a "secret function" in the past by using modifier keys bool showFunThing = (Control.ModifierKeys & Keys.Control) == Keys.Control; but wanted to get a bit more secretive (without the modifier keys) I just wanted the form to detect a certain word typed without any input ... I've built a method that I think should do it: private StringBuilder _pressedKeys = new StringBuilder(); protected override void OnKeyDown(KeyEventArgs e) { const string kWord = "fun"; char letter = (char)e.KeyValue; if (!char.IsLetterOrDigit(letter)) { return; } _pressedKeys.Append(letter); if (_pressedKeys.Length == kWord.Length) { if (_pressedKeys.ToString().ToLower() == kWord) { MessageBox.Show("Fun"); _pressedKeys.Clear(); } } base.OnKeyDown(e); } Now I need to wire it up but I can't figure out how I'm supposed to raise the event in the form designer ... I've tried this: this.KeyDown +=new System.Windows.Forms.KeyEventHandler(OnKeyDown); and a couple of variations on this but I'm missing something because it won't fire (or compile). It tells me that the OnKeyDown method is expecting a certain signature but I've got other methods like this where I haven't specified arguments. I fear that I may have got myself confused so I am turning to SO for help ... anyone?

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• Arduino variable going blank after the first pass

  - by user541597

  I have an Arduino sketch that takes a timet and when that timet is equal to the current time it sets the new timet to timet + 2. For example: char* convert(char* x, String y) { int hour; int minute; sscanf(x, "%d:%d", &hour, &minute); char buf[6]; if (y == "6") { if (hour > 17) { hour = (hour+6)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } else if (hour < 18) { //hour = hour + 6; minute = (minute + 2); snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "12") { if (hour > 11) { hour = (hour+12)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } else if (hour < 12) { hour = hour + 12; snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "24") { hour = (hour+24)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } return buf; } The sketch starts for example at 1:00am. timet is set to 1:02, at system time 1:02 timet is equal to the system time. My loops looks like this: if (timet == currenttime) { timet = convert(timet) } Whenever I check the value of timet it should equal 1:04, however I get the correct value at the first run after the execution of convert, however every time after that my timet value is blank. I tried changing the code instead of using the if loop. I only run the convert function when I send for example t through the serial monitor. This works fine and outputs the correct timet after the execution of the convert function, So I figured the problem is in the if loop... Any ideas?

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• Boost::Asio - Remove the "null"-character in the end of tcp packets.

  - by shump

  I'm trying to make a simple msn client mostly for fun but also for educational purposes. And I started to try some tcp package sending and receiving using Boost Asio as I want cross-platform support. I have managed to send a "VER"-command and receive it's response. However after I send the following "CVR"-command, Asio casts an "End of file"-error. After some further researching I found by packet sniffing that my tcp packets to the messenger server got an extra "null"-character (Ascii code: 00) at the end of the message. This means that my VER-command gets an extra character in the end which I don't think the messenger server like and therefore shuts down the connection when I try to read the CVR response. This is how my package looks when sniffing it, (it's Payload): (Hex:) 56 45 52 20 31 20 4d 53 4e 50 31 35 20 43 56 52 30 0a 0a 00 (Char:) VER 1 MSNP15 CVR 0... and this is how Adium(chat client for OS X)'s package looks: (Hex:) 56 45 52 20 31 20 4d 53 4e 50 31 35 20 43 56 52 30 0d 0a (Char:) VER 1 MSNP15 CVR 0.. So my question is if there is any way to remove the null-character in the end of each package, of if I've misunderstood something and used Asio in a wrong way. My write function (slightly edited) looks lite this: int sendVERMessage() { boost::system::error_code ignored_error; char sendBuf[] = "VER 1 MSNP15 CVR0\r\n"; boost::asio::write(socket, boost::asio::buffer(sendBuf), boost::asio::transfer_all(), ignored_error); if(ignored_error) { cout << "Failed to send to host!" << endl; return 1; } cout << "VER message sent!" << endl; return 0; } And here's the main documentation on the msn protocol I'm using. Hope I've been clear enough.

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• Error in VC++ for code that looks perfectly good C++?

  - by Ram Bhat

  Hey guys. Check out this piece of sample code. #include "stdafx.h" #include<conio.h> #include<string.h> class person{ private char name[20]; private int age; public void setValues(char n[],int a) { strcpy(this->name,n); this->age=a; } public void display() { printf("\nName = %s",name); printf("\nAge = %d",age); } }; int _tmain(int argc, _TCHAR* argv[]) { person p; p.setValues("ram",20); p.display(); getch(); return 0; } I am getting the following errors : 1------ Build started: Project: first, Configuration: Debug Win32 ------ 1 first.cpp 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(9): error C2144: syntax error : 'char' should be preceded by ':' 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(10): error C2144: syntax error : 'int' should be preceded by ':' 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(12): error C2144: syntax error : 'void' should be preceded by ':' 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(17): error C2144: syntax error : 'void' should be preceded by ':' ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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• Parallel.For Batching

  - by chibacity

  Is there built-in support in the TPL for batching operations? I was recently playing with a routine to carry out character replacement on a character array which required a lookup table i.e. transliteration: for (int i = 0; i < chars.Length; i++) { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } } I could see that this could be trivially parallelized, so jumped in with a first stab which I knew would perform worse as the tasks were too fine-grained: Parallel.For(0, chars.Length, i => { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } }); I then reworked the algorithm to use batching so that the work could be chunked onto different threads in less fine-grained batches. This made use of threads as expected and I got some near linear speed up. I'm sure that there must be built-in support for batching in the TPL. What is the syntax, and how do I use it? const int CharBatch = 100; int charLen = chars.Length; Parallel.For(0, ((charLen / CharBatch) + 1), i => { int batchUpper = ((i + 1) * CharBatch); for (int j = i * CharBatch; j < batchUpper && j < charLen; j++) { char replaceChar; if (lookup.TryGetValue(chars[j], out replaceChar)) { chars[j] = replaceChar; } } });

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• How safe and reliable are C++ String Literals?

  - by DoctorT

  So, I'm wanting to get a better grasp on how string literals in C++ work. I'm mostly concerned with situations where you're assigning the address of a string literal to a pointer, and passing it around. For example: char* advice = "Don't stick your hands in the toaster."; Now lets say I just pass this string around by copying pointers for the duration of the program. Sure, it's probably not a good idea, but I'm curious what would actually be going on behind the scenes. For another example, let's say we make a function that returns a string literal: char* foo() { // function does does stuff return "Yikes!"; // somebody's feeble attempt at an error message } Now lets say this function is called very often, and the string literal is only used about half the time it's called: // situation #1: it's just randomly called without heed to the return value foo(); // situation #2: the returned string is kept and used for who knows how long char* retVal = foo(); In the first situation, what's actually happening? Is the string just created but not used, and never deallocated? In the second situation, is the string going to be maintained as long as the user finds need for it? What happens when it isn't needed anymore... will that memory be freed up then (assuming nothing points to that space anymore)? Don't get me wrong, I'm not planning on using string literals like this. I'm planning on using a container to keep my strings in check (probably std::string). I'm mostly just wanting to know if these situations could cause problems either for memory management or corrupted data.

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• STL vector performance

  - by iAdam

  STL vector class stores a copy of the object using copy constructor each time I call push_back. Wouldn't it slow down the program? I can have a custom linkedlist kind of class which deals with pointers to objects. Though it would not have some benefits of STL but still should be faster. See this code below: #include <vector> #include <iostream> #include <cstring> using namespace std; class myclass { public: char* text; myclass(const char* val) { text = new char[10]; strcpy(text, val); } myclass(const myclass& v) { cout << "copy\n"; //copy data } }; int main() { vector<myclass> list; myclass m1("first"); myclass m2("second"); cout << "adding first..."; list.push_back(m1); cout << "adding second..."; list.push_back(m2); cout << "returning..."; myclass& ret1 = list.at(0); cout << ret1.text << endl; return 0; } its output comes out as: adding first...copy adding second...copy copy The output shows the copy constructor is called both times when adding and when retrieving the value even then. Does it have any effect on performance esp when we have larger objects?

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• why BOOST_FOREACH cannot handle const boost::ptr_map?

  - by psaghelyi

  void main() { typedef boost::ptr_map<int, char> MyMap; MyMap mymap; mymap[1] = 'a'; mymap[2] = 'b'; mymap[3] = 'c'; BOOST_FOREACH(MyMap::value_type value, mymap) { std::cout << value.first << " " << value.second << std::endl; } MyMap const & const_mymap = mymap; BOOST_FOREACH(MyMap::value_type value, const_mymap) { std::cout << value.first << " " << value.second << std::endl; } } The following error message comes from GCC at the second BOOST_FOREACH error: conversion from 'boost::ptr_container_detail::ref_pair<int, const char* const>' to non-scalar type 'boost::ptr_container_detail::ref_pair<int, char* const>' requested I reckon that this is the weakness of the pointer container's ref_pair...

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• Getting ellipses function parameters without an initial argument

  - by Tox1k

  So I've been making a custom parser for a scripting language, and I wanted to be able to pass only ellipses arguments. I don't need or want an initial variable, however Microsoft and C seem to want something else. FYI, see bottom for info. I've looked at the va_* definitions #define _crt_va_start(ap,v) ( ap = (va_list)_ADDRESSOF(v) + _INTSIZEOF(v) ) #define _crt_va_arg(ap,t) ( *(t *)((ap += _INTSIZEOF(t)) - _INTSIZEOF(t)) ) #define _crt_va_end(ap) ( ap = (va_list)0 ) and the part I don't want is the v in va_start. As a little background I'm competent in goasm and I know how the stack works so I know what's happening here. I was wondering if there is a way to get the function stack base without having to use inline assembly. Ideas I've had: #define im_va_start(ap) (__asm { mov [ap], ebp }) and etc... but really I feel like that's messy and I'm doing it wrong. struct function_table { const char* fname; (void)(*fptr)(...); unsigned char maxArgs; }; function_table mytable[] = { { "MessageBox", &tMessageBoxA, 4 } }; ... some function that sorts through a const char* passed to it to find the matching function in mytable and calls tMessageBoxA with the params. Also, the maxArgs argument is just so I can check that a valid number of parameters is being sent. I have personal reasons for not wanting to send it in the function, but in the meantime we can just say it's because I'm curious. This is just an example; custom libraries are what I would be implementing so it wouldn't just be calling WinAPI stuff. void tMessageBoxA(...) { // stuff to load args passed MessageBoxA(arg1, arg2, arg3, arg4); } I'm using the __cdecl calling convention and I've looked up ways to reliably get a pointer to the base of the stack (not the top) but I can't seem to find any. Also, I'm not worried about function security or typechecking.

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• Copy constructor demo (crashing...)

  - by AKN

  Here is the program... class CopyCon { public: char *name; CopyCon() { name = new char; } CopyCon(const CopyCon &objCopyCon) { name = new char; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete name; name = NULL; } } }; int main() { CopyCon objCopyCon1; objCopyCon1.name = "Hai"; CopyCon objCopyCon2(objCopyCon1); objCopyCon1.name = "Hello"; cout<<objCopyCon2.name<<endl; return 0; } Once the code execution completes, when the destructor called, it crashes on 'delete' saying... Debug Error! Program: ... HEAP CORRUPTION DETECTED: after Normal block (#124) at 0x00366990. CRT detected that the application wrote to memory after end of heap buffer. (Press Retry to debug the application) Don't we have to clear the heap memory in destructor. What's wrong with this program? Pls someone help! Copy constructor works perfectly as intended. But still... !?

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• Compiler turning a string& into a basic_string<>&

  - by Shtong

  Hello I'm coming back to C++ after long years spent on other technologies and i'm stuck on some weird behavior when calling some methods taking std::string as parameters : An example of call : LocalNodeConfiguration *LocalNodeConfiguration::ReadFromFile(std::string & path) { // ... throw configuration_file_error(string("Configuration file empty"), path); // ... } When I compile I get this (I cropped file names for readability) : /usr/bin/g++ -g -I/home/shtong/Dev/OmegaNoc/build -I/usr/share/include/boost-1.41.0 -o CMakeFiles/OmegaNocInternals.dir/configuration/localNodeConfiguration.cxx.o -c /home/shtong/Dev/OmegaNoc/source/configuration/localNodeConfiguration.cxx .../localNodeConfiguration.cxx: In static member function ‘static OmegaNoc::LocalNodeConfiguration* OmegaNoc::LocalNodeConfiguration::ReadFromFile(std::string&)’: .../localNodeConfiguration.cxx:72: error: no matching function for call to ‘OmegaNoc::configuration_file_error::configuration_file_error(std::string, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)’ .../configurationManager.hxx:25: note: candidates are: OmegaNoc::configuration_file_error::configuration_file_error(std::string&, std::string&) .../configurationManager.hxx:22: note: OmegaNoc::configuration_file_error::configuration_file_error(const OmegaNoc::configuration_file_error&) So as I understand it, the compiler is considering that my path parameter turned into a basic_string at some point, thus not finding the constructor overload I want to use. But I don't really get why this transformation happened. Some search on the net suggested me to use g++ but I was already using it. So any other advice would be appreciated :) Thanks

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• Enumeration trouble: redeclared as different kind of symbol

  - by Matt

  Hello all. I am writing a program that is supposed to help me learn about enumeration data types in C++. The current trouble is that the compiler doesn't like my enum usage when trying to use the new data type as I would other data types. I am getting the error "redeclared as different kind of symbol" when compiling my trangleShape function. Take a look at the relevant code. Any insight is appreciated! Thanks! (All functions are their own .cpp files.) header file #ifndef HEADER_H_INCLUDED #define HEADER_H_INCLUDED #include <iostream> #include <iomanip> using namespace std; enum triangleType {noTriangle, scalene, isoceles, equilateral}; //prototypes void extern input(float&, float&, float&); triangleType extern triangleShape(float, float, float); /*void extern output (float, float, float);*/ void extern myLabel(const char *, const char *); #endif // HEADER_H_INCLUDED main function //8.1 main // this progam... #include "header.h" int main() { float sideLength1, sideLength2, sideLength3; char response; do //main loop { input (sideLength1, sideLength2, sideLength3); triangleShape (sideLength1, sideLength2, sideLength3); //output (sideLength1, sideLength2, sideLength3); cout << "\nAny more triangles to analyze? (y,n) "; cin >> response; } while (response == 'Y' || response == 'y'); myLabel ("8.1", "2/11/2011"); return 0; } triangleShape shape # include "header.h" triangleType triangleShape(sideLenght1, sideLength2, sideLength3) { triangleType triangle; return triangle; }

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