fprintf printing garbage to txt file

Question

I'm having trouble with strings and c.

I'm trying to do something very simple: converting an int into a string and printing it into a txt file in the following fashion.

const char * test_string() {
    char s[5];
    int num = 123;
    sprintf(s, "%d", num);
    return s;
}

int save() {
    FILE *fh = fopen("test.txt", "w");
    const char * text = test_string();
    fprintf(fh, "%s", text);
    fclose(fh);
}

Yet, for this simple task, I'm getting the following result:

Üþ(

I'd like some assistance with this problem. Thanks in advance.

Returning the address of a local variable from a function has undefined behaviour, because the variable is no longer alive after the function has returned. — Kerrek SB, Sep 27 '16 at 22:28
@KerrekSB: We should add a dup to this question to the info-page. That question is asked every few days. — too honest for this site, Sep 27 '16 at 22:34
@miroki123: If you have a good C book and read it **carefully**, it is actually not. — too honest for this site, Sep 27 '16 at 22:35
You could also look at [Difference between dangling pointer and memory leak?](http://stackoverflow.com/questions/13132798/difference-between-dangling-pointer-and-memory-leak) — Jonathan Leffler, Sep 27 '16 at 22:35

score 4 · Accepted Answer · answered Sep 27 '16 at 22:29

4

s is a local variable in test_string, so it is destroyed when test_string returns. Then, you try to print the value of a variable that no longer exists.

answered Sep 27 '16 at 22:29

user253751

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The mess it prints is a string interpretation of whatever happens to have filled that space in the meantime. – Carcigenicate Sep 27 '16 at 22:33

fprintf printing garbage to txt file

1 Answers1