Error while reading character using gets function

Question

I am writing a string to a file. But only the first part of the string is only inserted to file. Others are missing. For eg: If I write "I Like Flowers", "I" is only written into file.

    #include <stdio.h>
int main()
{
        char string[50];
        int marks,i,n;
        FILE *fptr; fptr=(fopen("string.txt","w"));
        if(fptr==NULL){
                printf("Error!");
                return 0;
        }
        printf("Enter a string : \n");
        scanf("%s", string);
        //fprintf(fptr,"%s",string);
        fwrite(string, 1, sizeof(string), fptr);

        fclose(fptr);
        return 0;
}

why this is downvoted? It would be helpful, if you can specify a reason before Downvoting. — jay, Dec 13 '13 at 11:21
Programmer should never assume problem with standard library, the problem always with the code you wrote. Well, there is a small, nearly non-existent chance to hit the stdlib bug, but you have to be 500% sure it is not your fault before assuming this. — qrdl, Dec 13 '13 at 11:30
Sorry. Actually I wrote the question about the bug in my program. Will change the title soon. — jay, Dec 13 '13 at 12:28

hmjd · Accepted Answer · 2013-12-13T11:06:09.057

6

The scanf() will stop reading at the first space: that is the problem. The scanf("%s") only reads the I from standard input. To read the entire line use fgets() instead. Use strlen() to write only what was read instead of using sizeof(string).

edited Dec 13 '13 at 11:06

answered Dec 13 '13 at 11:00

hmjd

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Thanks. But after adding fgets the program is just exiting before I enter any string. Is this the correct syntax? printf("Enter a string : \n"); fgets(string, 100, fptr); – jay Dec 13 '13 at 11:10
`fgets(string, sizeof(string), stdin);`: note `stdin`. _Always_ check return values to ensure success of a function. – hmjd Dec 13 '13 at 11:16
Again error. Segmentation fault: 11. Now the program is like this : fgets(string, sizeof(string), stdin); fwrite(string, sizeof(string), strlen(string), fptr); fclose(fptr); – jay Dec 13 '13 at 11:20
Read [`fwrite()`](http://en.cppreference.com/w/c/io/fwrite). I meant `strlen()` _instead of_ `sizeof()`. – hmjd Dec 13 '13 at 11:27
You don't want to use `sizeof(string)` *and* `strlen(string)`, use `fwrite(string, 1, strlen(string), fptr);` instead. Otherwise you try to write (and thus read from `string`) `sizeof(string)` * `strlen(string)` characters, which is more than is allocated there. – Kninnug Dec 13 '13 at 11:27
"The scanf() will stop reading at the first space" mis-leads a bit. `scanf("%s")` scans (and does not save white space), then scans and saves non-white space, then "stop reading at the first space". – chux - Reinstate Monica Dec 13 '13 at 13:31

score 1 · Answer 2 · edited Aug 30 '15 at 13:55

1

In your code scanf("%s",string) only takes the string up to the first space. To read the total string "I Like Flowers", you have to use the scanf function like this:

scanf("%[^\n]s,string);

it will work.

edited Aug 30 '15 at 13:55

Matthieu M.

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answered Aug 30 '15 at 13:42

Bandi Ravi Teja Naidu

11
1

Error while reading character using gets function

2 Answers2