Why doesnt my C program work? reading from a file

Question

Im new to C programming and Im trying to make a program that reads the context of a file named input.

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char ch;
    FILE *in;
    in = fopen("input","r");
    printf("The contents of the file are\n");
    fscanf(in,"%c",&ch);
    printf("%c",ch);
    fclose(in);
    return 0;
}

please describe the contents of the `input` file, and what behavior is actually happening, and what you expect to happen instead. — Mike Frysinger, Mar 24 '16 at 05:32
the input file just has random text to test for example, Hello World — Eric Z, Mar 24 '16 at 05:33
i would like it to print the contents of the file on screen(terminal) — Eric Z, Mar 24 '16 at 05:37
use loop E.g `while(1==fscanf(in,"%c",&ch)) printf("%c",ch);` — BLUEPIXY, Mar 24 '16 at 05:41
Check the answer on the following link my help. http://stackoverflow.com/questions/36189108/very-basic-trying-to-read-from-a-text-file-with-numbers-and-store-them-in-an-ar/36189728#36189728 — Awad A. Bekhet, Mar 24 '16 at 05:46
What does this code do? it works now but i dont know what this part does 1==fscanf? while(1==fscanf(in,"%c",&ch)) { printf("%c",ch); } — Eric Z, Mar 24 '16 at 06:08

score 1 · Answer 1 · answered Mar 24 '16 at 05:42

1

Your code is reading just the first character of the file. There is no loop to read over the complete file. Is that what you intended?

Also, check if the file open was successful. Is the input file name "input" ?

answered Mar 24 '16 at 05:42

lamirap

510
1
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8

Riken Shah · Answer 2 · 2016-03-24T06:15:13.767

0

Try this -

char text[100];
fp=fopen(name,"r");
fgets(text,sizeof(text),fp); //99 is maximum number of characters to be printed including newline, if it exists
printf("%s\n",text);
fclose(fp);

edited Mar 24 '16 at 06:15

answered Mar 24 '16 at 05:38

Riken Shah

3,022
5
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1

"100 is maximum number of characters to be printed" No. One byte is for terminating null-character, so the maximum is 99 characters including the newline character if it exists. – MikeCAT Mar 24 '16 at 05:46
1

Also using magic number is not good and the line using `fgets()` should be `fgets(text,sizeof(text),fp);` Adding error check will make the code better. – MikeCAT Mar 24 '16 at 05:54
`sizeof(100)` -> `sizeof text` – M.M Mar 24 '16 at 06:14

score 0 · Answer 3 · answered Mar 24 '16 at 06:26

Suppose the content of file input is:

Hello World

You can try the following code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char ch;
    FILE *in;
    in = fopen("input","r");
    printf("The contents of the file are\n");
    while(fscanf(in, "%c", &ch) != EOF)
    {
        printf("%c",ch);
    }
    fclose(in);
    return 0;
}

Output:

The contents of the file are
Hello World

score -1 · Answer 4 · answered Mar 24 '16 at 06:05

You should use this:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char ch;
    FILE *in;

    /*Don't forget the extension (.txt)*/
    if(in = fopen("input.txt","r") == NULL);     
    {
        printf("File could not be opened\n");
    }
    else                                 
    {
       printf("The contents of the file are\n");
       /*I assume that you are reading char types*/
       fscanf(in,"%c",&ch);                   

       /*Check end-of-file indicator*/
       while(!feof(in))                      
       {
           printf("%c",ch);
           fscanf(in,"%c",&ch); 
       }
    }

    fclose(in);
    return 0;
}

You should bear in mind verify whether the file is open or not, it is always a good practice.

It would be better to not test `feof`. [See here](http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong) for explanation. — M.M, Mar 24 '16 at 06:13

Why doesnt my C program work? reading from a file

4 Answers4