How to remove the Debug Assertion Error in Visual studio

Question

I have a program to read the names of files in a directory. The code runs in the CodeBlocks IDE but the same gives me a Debug Assertion Error when I run it in Visual Studio.

I have added _CRT_SECURE_NO_WARNINGS in the Preprocessor properties because without it strerror() gave me an error.

#include <windows.h>
#include <stdio.h>

void listdirs(wchar_t *dir, wchar_t *mask)
{
wchar_t *fspec1 = { L'\0' }, *fname = { L'\0' };
WIN32_FIND_DATA     dta;
HANDLE              hDta;
DWORD dLastError;
LPCWSTR fspec = reinterpret_cast<LPCWSTR>(fspec1);
char *buff = { '\0' };

swprintf(fspec1, 100, L"%s/%s", dir, mask);


if ((hDta = FindFirstFile(fspec, &dta)) == INVALID_HANDLE_VALUE) {

    dLastError = GetLastError();
  printf("The error : %s\n", strerror(dLastError));



}

else {
    do {
        if (!(dta.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY))
        {
            printf("%ws\n", dta.cFileName);
        }
        else
        {
        if (wcscmp(dta.cFileName,L".") !=0 && wcscmp(dta.cFileName,L"..")!=0)
            {
                swprintf(fname, 100,  L"%s", dta.cFileName);
                listdirs(fname, mask);
            }
        }
    } while (FindNextFile(hDta, &dta));

    FindClose(hDta);
}
}
int main (int argc, char *argv[])
{
    listdirs(L"C:\\windows\\system32\\Tasks", L"\\.*"); 
    return 0;
}

The output should either print an error message if it cannot access the folder or print the filenames. In either case, I only get a debug assertion error.

Answer 1

With the definitions

wchar_t *fspec1 = { L'\0' }, *fname = { L'\0' };

you say that both fspec1 and fname are pointers, pointing to NULL. Attempting to dereference these pointers in any way will lead to undefined behavior.

And you do dereference these pointers, and even attempt to write to where these null-pointers are pointing. For example with

swprintf(fspec1, 100, L"%s/%s", dir, mask);

You need to allocate memory for these pointers to actually point to. Or define them as suitably sized arrays:

wchar_t fspec1[100], fname[100];