Thread: unexpected result, no display of input string

Edit: Forget everything I just said. Your program is a mess. Here's a fixed version:

Code:

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

#define STRLENGTH 80
int main(int argc, char *argv[])
{
  FILE *out;
  char str[STRLENGTH];

  if((out = fopen("Text", "w+")) == NULL)
  {
    printf("Error in creating file\n");
    exit(1);
  }
  printf("Please enter the text to be inputed:\n");
  do
  {
    fgets(str, STRLENGTH, stdin);
    fputs(str, out);
    if(ferror(out))
      printf("Error");
  } while(*str != '\n');

  rewind(out);
  while(fgets(str, STRLENGTH, out))
  {
    if(feof(out))
      break;
    printf(str);
  }

  fclose(out);
  return 0;
}

Stuff wrong in the original version:
- You used gets()! Evil! You had a serious buffer overrun vulnerability because of it.
- You tried reading from an output stream. Changing to mode "w+" fixes that.
- '/n' isn't even a real character.
- What's up with the infinite loop toward the end of your program? A more graceful way to not exit immediately is to just use a getchar(); call. Then press ENTER to continue.
- You didn't call fclose(out);. Open files are closed when the program exits, but it's good form to explicitly close open files.

Remember: Don't ever ever ever use gets(). Forget it even exists.

> printf(str); is perfectly legal.
Legal perhaps, but massively unwise, error prone and buggy.
All the user has to do is type in a % character, and you're in a world-of-pain as printf() wanders up the stack looking for non-existant parameters to unknown conversions.

> fgets(str, STRLENGTH, stdin)
This should be in a while loop, just like your 2nd use of fgets()

Originally Posted by itsme86

printf(str); is perfectly legal.

it might compile and "work" but its not standard
the first string is always the format string with printf, and as Salem pointed out, an input of "%" will cause you a world of pain.

$man 3 printf
[...]
SYNOPSIS
#include <stdio.h>

int printf(const char *format, ...);
int fprintf(FILE *stream, const char *format, ...);
int sprintf(char *str, const char *format, ...);
int snprintf(char *str, size_t size, const char *format, ...);

#include <stdarg.h>

int vprintf(const char *format, va_list ap);
int vfprintf(FILE *stream, const char *format, va_list ap);
int vsprintf(char *str, const char *format, va_list ap);
int vsnprintf(char *str, size_t size, const char *format, va_list ap);
[...]

edit: noting that constant strings are commonly printed as the format string since there isnt any (obvious) danger of a '%' jumping into the buffer.

Originally Posted by Perspective

it might compile and "work" but its not standard
the first string is always the format string with printf, and as Salem pointed out, an input of "%" will cause you a world of pain.


edit: noting that constant strings are commonly printed as the format string since there isnt any (obvious) danger of a '%' jumping into the buffer.

Of course it's standard! What on earth do you think a string literal is if not a string? ANY string may be use for the first argument. It's up to you to make your "string" valid, just like every call to every function. It's up to you to make sure you're passing what the function expects you to pass. It most definately is allowed by the standard.

Quzah.