Having trouble using the implementation of memmem() in windows

Question

When I use the function I only receive NULL, is there anything wrong that I do? I am trying to read a file in a binary way and then to find out if there is a specific signature there

Here is my code:

#include <stdio.h>
void *memmem(const void *haystack, size_t haystack_len, const void * const needle, const size_t needle_len);
#define TEXT2 "hey"

int main(void)
{   
    unsigned char* buffer = NULL;
    FILE* file = fopen("lol.txt", "rb");

    long bufferLen = 0;

    fseek(file, 0, SEEK_END);
    bufferLen = ftell(file);
    fseek(file, 0, SEEK_SET);

    buffer = (char*)calloc(bufferLen, sizeof(char));


    fread(buffer, sizeof(char), bufferLen, file);
    fclose(file);

    char *pos = memmem(buffer, bufferLen, TEXT2, sizeof(TEXT2));

    if (pos != NULL)
        printf("hey");

    getchar();
    return 0;
}


void *memmem(const void *haystack, size_t haystack_len, const void * const needle, const size_t needle_len)
{
    if (haystack == NULL) return NULL; // or assert(haystack != NULL);
    if (haystack_len == 0) return NULL;
    if (needle == NULL) return NULL; // or assert(needle != NULL);
    if (needle_len == 0) return NULL;

    for (const char *h = haystack; haystack_len >= needle_len; ++h, --haystack_len) 
    {
        if (!memcmp(h, needle, needle_len)) 
        {
            return h;
        }
    }
    return NULL;
}

I tried to do it, but it always returning me null is there any ideas? am I doing anything wrong?

I'm sure you can easily find a `memmem` implementation using google. — Jabberwocky, May 24 '19 at 15:39
@Jabberwocky I tried but didn't find any good enough implementation — id0 SI, May 24 '19 at 15:42
_"Good enough"_ in terms of what? Maybe you should ask about _that_. — Jabberwocky, May 24 '19 at 15:43
What did you do in which post?? What's wrong with the `memmem` implementations you have found? — Jabberwocky, May 24 '19 at 15:46
I found one in this post: https://stackoverflow.com/questions/2188914/c-searching-for-a-string-in-a-file But 'p++' didn't work for me visual studio wrote: "expression must be a pointer to a complete object type" — id0 SI, May 24 '19 at 15:49
Possible duplicate of [Searching text in binary data](https://stackoverflow.com/questions/6135643/searching-text-in-binary-data) — Eugene Sh., May 24 '19 at 16:08
That doesn't make it less duplicate. You either use `memmem`, or implement it yourself or use one of the string matching algorithms there. No other magic is available. — Eugene Sh., May 24 '19 at 16:13
@EugeneSh. I posted my code I would be glad if u could check it up — id0 SI, May 24 '19 at 16:14
Then please describe what is the problem with this code. Better edit the question as it is currently not reflecting the actual problem. — Eugene Sh., May 24 '19 at 16:15
Better, retracted my vote. You might want to start with small inputs and step through with a debugger. — Eugene Sh., May 24 '19 at 16:22
I tried to search only 'h' or 'e' but it didn't succeed @EugeneSh. — id0 SI, May 24 '19 at 16:25
I found a fix, thank you so much for your help you really made me better in asking for help! @EugeneSh. — id0 SI, May 24 '19 at 16:26

score 2 · Answer 1 · answered May 24 '19 at 16:24

char *pos = memmem(buffer, bufferLen, TEXT2, sizeof(TEXT2));
//                                           ^^^^^^^^^^^^^

sizeof "hey" is 4. "hey" has type char[4].

Replace with strlen("hey")

char *pos = memmem(buffer, bufferLen, TEXT2, strlen(TEXT2));

Having trouble using the implementation of memmem() in windows

1 Answers1