Can't read file in C using fread()-CodePudding

Program asks for input and stores it in a variable, then confirms the operation printing the content of the file. Or at least it had to, when the program ends it doesn't print the file content, I can't seem to find an answer, I've been looking in the docs but can't really figure it out.

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

int main(void)
{
    FILE * file1 = fopen(".out", "w ");

    char *s = malloc(513);
    fgets(s, 513, stdin);
    
    if (fprintf(file1, "%s", s) < 0)
    {
        printf("Something failed while writing to the file\n");
        return 1;
    }
    else
    {
        char *t = malloc(513);
        fread(t, sizeof(char), 1, file1);
        printf("Success! Input was: %s \n", t);
        return 0;
    }
}

P.S: Very new to C, though it may seem obvious for you I have no clue whatsoever.

CodePudding user response：

There are 2 issues here, 1 - you wrote to the file handler and you are trying to read from that point onwards - you didnt rewind the file pointer! 2 - you are just reading 1 character and not the amount you wrote to it!

#include <string.h>

...

        int n = strlen(s);
        rewind(file1);   // rewind before read 
        fread(t, sizeof(char), n, file1);   // read as much as you wrote

CodePudding user response：

Some problems in your code:

You are not checking the return value of fopen(), malloc(), fgets() and fread().
You are writing one character to the output stream, without rewinding it.

Here's how your code should look like:

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

int main(void)
{
    FILE * file1 = fopen(".out", "w ");
    if (!file1) {
        printf("Could not open file.\n");
        return 1;
    }

    const size_t n = 513; // Use constants, not litterals.
    char *s = malloc(sizeof(char) * n);
    if (!s) {
        printf("Internal error.\n");
        fclose(file1);
        return 1;
    }
    
    if (!fgets(s, n, stdin)) {
        printf("Input failed.\n");
        fclose(file1);
        return 1;
    }
    
    if (fprintf(file1, "%s", s) < 0) {
        printf("Something failed while writing to the file\n");
        fclose(file1);
        return 1;
    }
    
    char *t = malloc(sizeof(char) * n);
    if (!t) {
        printf("Internal error.\n");
        fclose(file1);
        return 1;
    }
    
    rewind(file1);
    
    int ret = fread(t, sizeof(char), n, file1); // Read n characters, not 1.
    if (ret != strlen(s)) {
        if (feof(file1)) {
            printf("Error reading .out: unexpected end of file.\n");
        } else if (ferror(file1)) {
            perror("Error reading .out");
        }
        fclose(file1);
        return 1;
    }
    
    printf("Success! Input was: %s \n", t);
}