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• How can I notify an application of a programmatically set scrollbar value?

  - by Frerich Raabe

  My code involves standard Scroll Bar control and it happens that I need to change its value programmatically in some cases. I do this using SetScrollInfo function, as in this example: void setScrollBarValue( HWND scrollBar, int value ) { SCROLLINFO si = { sizeof( SCROLLINFO ); } si.fMask = SIF_POS; si.nPos = value; ::SetScrollInfo( scrollBar, SB_CTL, &si, true /* redraw */ ); } This appears to work fine (the thumb of the scrollbar moves around) but it fails to notify the rest of the application of the new scrollbar value. For instance, an edit control which uses the scroll bar (much like in the Windows notepad application) fails to scroll around because it doesn't get notified about the new scrollbar value. In case it matters: the scrollbar I'm modifying is not in the same process as the above setScrollBarValue function. Does anybody know how to achieve this?

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• how to allocate memory for struct itself, and its members

  - by Jack

  I have this struct: struct foo { char *a; char *b; char *c; char *d; }; it's possible allocate space for struct itself and its members instead of e.g, struct foo f; f.a = malloc(); f.b = malloc(); f.c = malloc(); f.d = malloc(); strcpy(f.a, "a"); strcpy(f.b, "b"); //.. something like this(of couse that it doesn't works): struct foo f = malloc(sizeof(struct f)); strpcy(f.a, "a"); //etc

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• How to determine IP used by client connecting to INADDR_ANY listener socket in C

  - by codebox_rob

  I have a network server application written in C, the listener is bound using INADDR_ANY so it can accept connections via any of the IP addresses of the host on which it is installed. I need to determine which of the server's IP addresses the client used when establishing its connection - actually I just need to know whether they connected via the loopback address 127.0.0.1 or not. Partial code sample as follows (I can post the whole thing if it helps): static struct sockaddr_in serverAddress; serverAddress.sin_family = AF_INET; serverAddress.sin_addr.s_addr = INADDR_ANY; serverAddress.sin_port = htons(port); bind(listener, (struct sockaddr *) &serverAddress, sizeof(serverAddress)); listen(listener, CONNECTION_BACKLOG); SOCKET socketfd; static struct sockaddr_in clientAddress; ... socketfd = accept(listener, (struct sockaddr *) &clientAddress, &length);

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• allocator with no template

  - by Merni

  Every stl container take an allocator as a second object, template < class T, class Allocator = allocator<T> > class vector; If you write your own class It is possible to use your own allocator. But is it possible to write your own allocator without using templates? For example, writing this function is not easy if you are not allowed to use templates pointer allocate(size_type n, const_pointer = 0) { void* p = std::malloc(n * sizeof(T)); if (!p) throw std::bad_alloc(); return static_cast<pointer>(p); } Because how could you know the size of T?

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• Why do i get segfault at the end of the application after everything's beed done properly ?

  - by VaioIsBorn

  #include <string.h> #include <stdlib.h> #include <stdio.h> int main(void) { unsigned char *stole; unsigned char pass[] = "m4ak47"; printf("Vnesi password: \t"); scanf("%s", stole); if(strncmp(stole, pass, sizeof(pass)) != 0) { printf("wrong password!\n"); exit(0); } else printf("Password correct\n"); printf("some stuf here...\n\n"); return 0; } This program is working nice, but with one problem - if the password is correct then it DOES do the printing of 'some stuf here...' but it also shows me segmentation fault error at the end. Why ?

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• What's the difference between initializing this structure with these strategies?

  - by mystify

  // the malloc style, which returns a pointer: struct Cat *newCat = malloc(sizeof(struct Cat)); // no malloc...but isn't it actually the same thing? uses memory as well, or not? struct Cat cat = {520.0f, 680.0f, NULL}; Basically, I can get a initialized structure in these two ways. My guess is: It's the same thing, but when I use malloc I also have to free() that. In the second case I don't have to think about memory, because I don't call malloc. Maybe. When should I use the malloc style, and when the other?

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• C: Reading file with a starting point

  - by Shinka

  A simple question but I can't find the answer in my book. I want to read a binary file to seed a random number generator, but I don't want to seed my generator with the same seed each time I call the function, so I will need to keep a variable for my position in the file (not a problem) and I would need to know how to read a file starting a specific point in the file (no idea how). The code: void rng_init(RNG* rng) { // ... FILE *input = fopen("random.bin", "rb"); unsigned int seed[32]; fread(seed, sizeof(unsigned int), 32, input); // seed 'rng'... fclose(input); }

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• Is it bad practice to declare an array mid-function...

  - by Maximus

  In C, which would be more proper... void MyFunction() { int* array; int size; //do a bunch of stuff size = 10; array = (int*)(sizeof(int)*size); //do more stuff... //no longer need array... free(array); } Or is something like this okay? void MyFunction() { int size; //do a bunch of stuff size = 10; array[size]; //do more stuff... } The malloc uses the heap instead of the stack, so I suppose if you know size is going to be very large you'd want to malloc... but if you're quite certain size will be small enough, would the second method be reasonable?

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• CreateFile2 returns access denied error in Windows 8

  - by Liton

  I have written the following lines of code to open a file under InstalledFolder directory: Platform::String^ locationPath = Platform::String::Concat(Package::Current->InstalledLocation->Path, "\\Assets\\Logo.png"); CREATEFILE2_EXTENDED_PARAMETERS extendedParams = {0}; extendedParams.dwSize = sizeof(CREATEFILE2_EXTENDED_PARAMETERS); extendedParams.dwFileAttributes = FILE_ATTRIBUTE_NORMAL; extendedParams.dwFileFlags = FILE_FLAG_SEQUENTIAL_SCAN; extendedParams.dwSecurityQosFlags = SECURITY_ANONYMOUS; extendedParams.lpSecurityAttributes = nullptr; extendedParams.hTemplateFile = nullptr; Wrappers::FileHandle file( CreateFile2( locationPath->Data(), GENERIC_READ, 0, OPEN_EXISTING, &extendedParams ) ); DWORD e = GetLastError(); if (file.Get() == INVALID_HANDLE_VALUE) { throw ref new Platform::FailureException(); } The CreateFile2 returns access denied error. Can anyone please help me out? Thanks,

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• reading partially from sockets

  - by nomad.alien

  I'm having a little test program that sends a lot of udp packets between client-server-client (ping/pong test). The packets are fixed size on each run(last run is max allowable size of udp packet) I'm filling the packets with random data except for the beginning of each packet that contains the packet number. So I'm only interested to see if I receive all the packets back at the client. I'm using sendto() and recvfrom() and I only read the sizeof(packet_number) (which in this case is an int). What happens to the rest of the data? Does it end up in fairyland (gets discarded)? or does the new packet that arrives gets appended to this "old" data? (using linux)

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• behavior of memset

  - by Vinicius Horta

  Does this function has the same behavior that 'memset'? (Oops! Your question couldn't be submitted because: Your post does not have much context to explain the code sections; please explain your scenario more clearly. ) inline void SetZeroArray( void *vArray[], unsigned int uArraySize ) { for(unsigned i=0; i<=uArraySize; i++ ) vArray[i] = NULL; } int main( int argc, char *argv[] ) { unsigned int uLevels[500]; SetZeroArray( (void**)uLevels, 500 ); unsigned int ulRLevels[500]; memset( &ulRLevels, 0, sizeof( ulRLevels ) ); system("pause>nul"); return EXIT_SUCCESS; }

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• Visual Studio 2010 Compiling C code

  - by Corsen2000

  I have the following code snippet. This is a c file in visual studio 2010. If i try to compile this with the line: int hello = 10; commented out it will compile just fine. If I comment that line in it will not compile. Am I missing something or should I not be using Visual Studio 2010 to compile C code. If this is a Visual Studio problem can anyone recommend a easy to use IDE / Compiler that I can for C. Thank You int* x = (int*) calloc(1, sizeof(int)); *x = 5; //int hello = 10; printf("Hello World! %i", *x); getchar();

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• C input loop for shell

  - by AustinM

  So I'm working on creating a very simple C program that just preforms shell commands. This is what I have so far: #include <stdio.h> int main() { char input[30]; fputs("$ ", stdout); fflush(stdout); fgets(input, sizeof input, stdin); system(input); } It works, but only for one command. For example if I compile and type ./cmd I get the $ prompt. If I type ls I get what I'm supposed to get. But then it exits and goes back to the regular system shell. How can I make it so after the user types a command it goes back to the "$" input.

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• Array of datas returning issue, Overwriting

  - by sijith

  Hi, Please help me on this Here i want to save the converted data into new pointers. But everytime the data is overwriting with most recent data. Please check my code TCHAR nameBuffer[256]; //Globally Declared void Caller() { TCHAR* ptszSecondInFile= QStringToTCharBuffer(userName); TCHAR* ptszOutFile=QStringToTCharBuffer(Destinationfilename); } TCHAR *dllmerge::QStringToTCharBuffer( QString buffer ) { memset(nameBuffer, 0, sizeof(nameBuffer)); #if UNICODE _tcscpy_s(nameBuffer, _countof(nameBuffer), buffer.toUtf8()); #else _tcscpy_s(nameBuffer, _countof(nameBuffer), buffer.toLocal8Bit()); #endif _tprintf( _T( "nameBuffer %s\n" ), nameBuffer ); return nameBuffer; } I am gettting ptszSecondInFile and ptszOutFile both same answer. Is it possible to do with TCHAR* nameBuffer[256];

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• How can I find out how much memory an object of a C++ class consumes?

  - by Shadow

  Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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• How can I find out how much memory an instance of a C++ class consumes?

  - by Shadow

  Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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• MACRO Question: Returning pointer to a certain value

  - by Andrei Ciobanu

  Is it possible to write a MACRO that has a type and a value as its input parameters (MACRO(type,value)), and returns a valid pointer to a location that holds the submitted value. This macro should perform like the following function, but in a more generic manner: int *val_to_ptr(int val){ int *r = NULL; r = nm_malloc(sizeof(*r)); *r = val; return r; } Where nm_malloc() is a failsafe malloc. The Macro usage should be compatible with this usage: printf("%d",*MACRO(int,5)); Is it possible to achieve that ?

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• Read from file into pointer to struct

  - by cla barzu

  I need help with pointers in C. I have to read from a file, and fill an array with pointers to struct rcftp_msg . Since now I did the next things: struct rcftp_msg { uint8_t version; uint8_t flags; uint16_t len; uint8_t buffer[512]; }; struct rcftp_msg *windows [10]; pfile = fopen(file,"r"); // Open the file I have to read from the file into the buffer, but I don't know how to do it. I tried the next: for (i = 0; i <10; i++){ leng=fread (**windows[i]->buffer**,sizeof(uint8_t),512,pfile); } I think windows[i]-buffer is bad, cuz that don't work. Sorry for my bad English :(

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• How to compare two char* variables

  - by davit-datuashvili

  Suppose we have the following method (it is in c code): const char *bitap_search(const char *text, const char *pattern) My question is how can I compare text and pattern if they are char? This method is like a substring problem but I am confused a bit can I write in term of char such code? if (text[i]==pattern[i])? look i am interesting at this algorithm in java http://en.wikipedia.org/wiki/Bitap_algorithm how implement this in java? R = malloc((k+1) * sizeof *R); and please help me to translate this code in java

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• Operators vs Functions in C/C++

  - by user356106

  Someone recently asked me the difference between a C++ standard operator (e.g. new,delete,sizeof) and function (e.g. tan,delete, malloc). By "standard" I mean those provided by default by the compiler suite, and not user defined. Below were the answers I gave, though neither seemed satisfactory. (1) An operator doesn't need any headers to be included to use it : E.g. you can have a call to new without including any headers. However, a function (say free() ) does need headers included, compulsorily. (2) An operator is defined as such (ie as a class operator) somewhere in the standard headers. A function isn't. Can you critique these answers and give me a better idea of the difference?

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• Why did this code still work?

  - by bstullkid

  Some old code that I just came across: MLIST * new_mlist_link() { MLIST *new_link = (MLIST * ) malloc(sizeof(MLIST)); new_link->next = NULL; new_link->mapi = NULL; new_link->result = 0; } This was being called to build a linked list, however I noticed there is no statement: return new_link; Even without the return statement there, the list still got built properly. Why did this happen? EDT: Platform: Mandriva 2009 64bit Linux 2.6.24.7-server GCC 4.2.3-6mnb1

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• Printing escape character

  - by danutenshu

  When I am given "d""\"/""b", I need to print out the statement character for character. (d, b, a slash, a backslash, and 5 quotes) in C++. The only errors that show now are the lines if(i.at(j)="\\") and else if(i.at(j)="\""). Also, how should the outside double apostrophes be excluded? #include <iostream> #include <cstdlib> using namespace std; int main (int argc, const char* argv[] ) { string i= argv[1]; for (int j=0; j>=sizeof(i)-1; j++) { if(i.at(j)="\\") { cout << "\\"; } else if(i.at(j)="\"") { cout << "\""; } else { cout << i.at(j); } } return 0; }

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• I need to create a very large array of bits/boolean values. How would I do this in C/C++?

  - by Eddy

  Is it even possible to create an array of bits with more than 100000000 elements? If it is, how would I go about doing this? I know that for a char array I can do this: char* array; array = (char*)malloc(100000000 * sizeof(char)); If I was to declare the array by char array[100000000] then I would get a segmentation fault, since the maximum number of elements has been exceeded, which is why I use malloc. Is there something similar I can do for an array of bits?

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• Why does this program segfault

  - by Leda

  Upon compiling and running this small program to reverse a string, I get a Segmentation Fault before any output occurs. Forgive me if this is an obvious question, I'm still very new to C. #include <stdio.h> int reverse(char string[], int length); int main() { char string[] = "reversed"; printf("String at start of main = %s", string); reverse(string, sizeof(string)); printf("%s\n", string); return 0; } // Reverse string int reverse(char string[], int length) { int i; char reversed[] = {}; int temp; for(i = 0; i < length; ++i) { temp = string[i]; reversed[length - i] = temp; } return 0; }

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• How to check whether iterators form a contiguous memory zone?

  - by Vincent

  I currently have the following function to read an array or a vector of raw data (_readStream is a std::ifstream) : template<typename IteratorType> inline bool MyClass::readRawData( const IteratorType& first, const IteratorType& last, typename std::iterator_traits<IteratorType>::iterator_category* = nullptr ) { _readStream.read(reinterpret_cast<char*>(&*first), (last-first)*sizeof(*first)); return _readStream.good(); } First question : does this function seem ok for you ? As we read directly a block of memory, it will only work if the memory block from first to last is contiguous in memory. How to check that ?

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