CODEWITHSUNDEEP
cbinaryfilesfread
one
one

Reputation: 511

fread not reading the whole file as expected

I'm trying to read a large binary file in C. I wrote the following code:

FILE* f1 =  fopen("filename.exe", "rb");
    if(f1 != NULL)
    {
        fseek(f1,0,SEEK_END);
        long l = ftell(f1);
        fseek(f1,0,SEEK_SET);
        char * buf = (char *)malloc(l* sizeof(char));
        int k = fread(buf,sizeof(buf),1,f1);
        if(k != l)
            printf("the file was not read properly");
    }

Now, not only is k not equal to l, it is much smaller (l is ~99,000,000 while k is only 13).

Is it possible that fread is stopping because it reaches a NULL in the file? What can I do to avoid it?

Upvotes: 1

Views: 2433

Answers (1)

Charlie Burns
Charlie Burns

Reputation: 7044

fread returns the number of items read. In your case size is l, and the number is 1. fread will return 1. Swap the arguments l and 1.

If you really want to look for an ascii string inside a binary file you can do something like:

char *find = ....
int len = strlen(find);
char *end = (buf + l) - len;
for(char *p = buf; p < end; p++) {
    if(strncmp(p, find, len) == 0) {
        // you have found ascii string in buf
    }
}

If it's not an ascii string you are looking for use memcmp() instead of strncmp.

Upvotes: 2

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