Free fails with Access violation reading location

[tejaswini_g]

Can anyone help what is wrong in the following code snippet.

free (Filelist[i]);

fails with access violation error. Thanks in advance. int _tmain(int argc, TCHAR *argv[]) { int i =0; char ** Filelist; int iFileCountInFolder=0; int iFileSize = 0; _tcscpy(szDirpath,_T("C:\\BMPread_W\\TransitionEffects\\Images")); FileCountInDir(szDirpath,&iFileCountInFolder,&iFileSize); Filelist = (char**)malloc(iFileCountInFolder * sizeof(char *)); if(Filelist == NULL) { fprintf(stderr, "out of memory\n"); return; } for(i = 0; i < iFileCountInFolder; i++) { Filelist[i] = (char*)malloc((iFileSize * sizeof(char))+1); if(Filelist[i] == NULL) { fprintf(stderr, "out of memory\n"); return; } } FindFilesInDirectory(szDirpath, Filelist, &iFileCountInFolder); if (Filelist != NULL) { for ( i = 0; i < iFileCountInFolder ; i++)

//following line failing with access voilation
free (Filelist[i]);

free (Filelist); } return 0; }

[Richard Andrew x64]

First, put your code between <pre></pre> tags so that it's readable. Second, the code you cite as causing the error is not even in the snippet you show. :confused:

The difficult we do right away... ...the impossible takes slightly longer.

[tejaswini_g]

re posted.

[leon de boer]

The mallocs and frees are fine in concept the issue is deeper I suspect this is the problem

Filelist[i] = (char*)malloc((iFileSize * sizeof(char))+1);

iFileSize is initially set to zero and then passed in as a parameter to FileCountInDir which I guess is supposed to fill it in. But I find it really strange because that function is counting the directory entries from it's function name. Really the string space allocation should be the length of each individual directory entry name so I am not sure it should be a single value. For example a file "fred.bmp" should allocate 9 bytes (8+asciiz 0) while "afred.bmp" should allocate 10 bytes (9+asciiz 0) I fail to see how you are allocating them all as iFileSize unless that is the largest filename in the directory. And that leads to the answer for your fail that iFilesize must be coming back from FileCountInDir as -1 and that means you are allocating -1+1 = 0 bytes of memory which will fail in malloc returning NULL. Hence Filelist[i] would indeed be carrying NULL You can put protection to stop the error by doing this

if (FileList[i] != 0) free (Filelist[i]);

But as discussed I think you have serious issues with iFileSize

[Lost User]

If you are posting a lump of code a compile ready snippet helps everybody.

Peter Wasser "The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts." - Bertrand Russell

[Lost User]

I think you are on to it as the mallocs and frees seem OK. Unfortunately not enough information provided.

Peter Wasser "The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts." - Bertrand Russell

[tejaswini_g]

I am posting compiled code. As stated above Freelist[i] fails. Highlighted the statement causing error. #include <> // remove extra angle bracket for compilation #include <> #include <> #include <> void FreeMemory(char** myArray, int row); void FileCountInDir(const TCHAR* dirpath, int * filescount, int* filesize); void FindFilesInDirectory(const TCHAR* dirpath, char** filelist); int _tmain(int argc, TCHAR *argv[]) { int i =0; TCHAR szDirpath[MAX_PATH]; //TCHAR Filelist[100][MAX_PATH]; char ** Filelist; int iFileCountInFolder=0; int iFileSize = 0; _tcscpy(szDirpath,_T("C:\\BMPread_W\\TransitionEffects\\Images")); FileCountInDir(szDirpath,&iFileCountInFolder,&iFileSize); Filelist = (char**)malloc(iFileCountInFolder * sizeof(char *)); if(Filelist == NULL) { fprintf(stderr, "out of memory\n"); return 0; } for(i = 0; i < iFileCountInFolder; i++) { Filelist[i] = (char*)malloc((iFileSize * sizeof(char))+1); if(Filelist[i] == NULL) { fprintf(stderr, "out of memory\n"); return 0; } } FindFilesInDirectory(szDirpath, Filelist); for(i =0;i

[Lost User]

malloc()-ing 0 bytes doesn't return NULL when I test. This appears to be implementation dependent.

Peter Wasser "The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts." - Bertrand Russell

[Lost User]

Firstly you should employ assert() to help you. This is a classic situation where many asserts can assist. By the look of your code iFileCountInFolder can change during execution. If it does get bigger on the free than on the malloc then "poof".

Peter Wasser "The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts." - Bertrand Russell

[tejaswini_g]

iFileCountInFolder is always fixed, since the files in a folder are fixed , means no files are added at run time. I did not understand why the Free statement is failing.