CODEWITHSUNDEEP
cfiledetect
Archie
Archie

Reputation: 5

Why I couldnt detect my file is empty or not in C?

I tried several ways to do it but I couldnt. Code interview:

    file = fopen(filename,"r");
    int size=0;
    if (file == NULL){
        printf("couldnt open: %s\n",filename);
    }
    else if(size==0){
        fseek(file,0,SEEK_END);
        size = ftell(file);
        fclose(file);
        if (size ==0){
            printf("empty");
        }
    }

I also tried to feof function, foef(file) always returns same value it doesnt care about file is empty or not. Any help?

Upvotes: 0

Views: 124

Answers (1)

MikeCAT
MikeCAT

Reputation: 75062

You opened the file in text mode, then used fseek() with SEEK_END.

On the other hand, the standard says that only SEEK_SET should be used for fseek() with text stream.

Therefore, your code invokes undefined behavior.

Quote from N1570 7.21.9.2 The fseek function:

4 For a text stream, either offset shall be zero, or offset shall be a value returned by an earlier successful call to the ftell function on a stream associated with the same file and whence shall be SEEK_SET.

Quote from N1570 4. Conformance:

2 If a ‘‘shall’’ or ‘‘shall not’’ requirement that appears outside of a constraint or runtime- constraint is violated, the behavior is undefined.

Upvotes: 3

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