When fputs is used directly for writing character array in a file, a different format of text is stored

Question

When I used fputs() to directly store a character array in a file, it stored this in the file:

ÈLwìþ(

Why was that?

#include <stdio.h>

int main()
{
    FILE *p;
    p=fopen("pa.txt","w+");
    char name[100];
    printf("Enter a string :");
    fputs(name,p);
    fclose(p);
    getchar();
    return 0;
}

When I take input in name using scanf() or gets(), the correct text is stored but when directly use fputs() is used it stored in an unusual format. Why does this happen?

You mean "why does accessing an uninitialized variable lead to unexpected consequences"? — Mr. Llama, Jun 10 '15 at 18:48
See also [Why `gets()` is so dangerous it should never be used?](http://stackoverflow.com/questions/1694036/why-is-the-gets-function-dangerous-why-should-it-not-be-used) — Jonathan Leffler, Aug 22 '15 at 17:26

P.P · Answer 1 · 2015-06-10T19:02:37.413

When I take input in name using scanf() or gets() correct text is stored but when directly fputs() is used it stored in unusual format. Why this happens ?

Accessing uninitialized variable p is undefined behaviour as its value indeterminate as per C standard. There's no explanation for why it happens. Just don't do that.

6.7.9 Initialization, (C11 draft)

If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate.

And indeterminate is defined as:

3.19.2 indeterminate
value either an unspecified value or a trap representation

Note that function gets() has been removed from the recent C standard (C11) and it has never been a safe anyway due to its buffer overflow issues.

score 1 · Accepted Answer · answered Jun 10 '15 at 18:52

1

When I take input in name using scanf() or gets() correct text is stored but when directly fputs() is used it stored in unusual format. Why this happens ?

You haven't read the data from stdin before writing it out using fputs.

Use:

fgets(name, sizeof(name), stdin);

and then:

fputs(name, p);

answered Jun 10 '15 at 18:52

R Sahu

204,454
14
159
270

I also don't understand when I compile and run this code it asks for input and takes input when I don't use scanf() or gets() . – ameyCU Jun 11 '15 at 04:52
1

@ameyCU, the input is processed by `getchar()`, which reads just one character. The rest are discarded since the program terminates after that. – R Sahu Jun 11 '15 at 05:20

score 0 · Answer 3 · answered Jun 10 '15 at 18:57

You have opened char array but you haven't used it. Analyze the code you will understand.

#include <stdio.h>
int main()
{
    char name[100];

    FILE *p;

    p=fopen("pa.txt","w+");

    if(!p) {
        perror("Error writing");
        return -1;
    }

    printf("Enter a string :");
    scanf("%s",name);
    fputs(name,p);

    fclose(p);

    return 0;
}

When fputs is used directly for writing character array in a file, a different format of text is stored

3 Answers3