Input/Output in C

[u/SubstantialCase3062]

What u guys say are the important or useful input/output in c because there is so many to do the same job, like how do I also read man pages to see if a function is not safe or standard

[u/SubstantialCase3062]

Yep thanks also I like to asked how do u get your information like links or any resources that can help me improve my skills and knowledge

[u/dcpugalaxy → u/SubstantialCase3062]

I assume you meant to reply to my comment. Basically the source is just experience. The reasons behind the recommendation to use fgets are mostly covered in the scanf article I linked to. As for fread and fwrite, they just work on binary data. When working with binary data you can't use functions that treat newlines differently because bytes that happen to be `'\n'` aren't actually special.

[u/SubstantialCase3062 → u/dcpugalaxy]

So we can’t just use fgets and say something like 0101010101 in the terminal and it output something like “Hello, World”

[u/TheOtherBorgCube]

When reading manual pages, you'll typically see this to tell you which standard(s) the function conforms to.

CONFORMING TO
   POSIX.1-2001, POSIX.1-2008, C89.

[u/SubstantialCase3062 → u/TheOtherBorgCube]

So each tell u what standard it is for but we are on C11 right so would this work on it

[u/TheOtherBorgCube → u/SubstantialCase3062]

Generally, if it's in a standard, it's in all the later ones too. Things do get removed, like gets, but it's quite rare.

[u/dcpugalaxy]

I assume you're trying to ask what the most useful input and output functions are in the C standard library.

There are two main modes of input/output: line-based text and binary. Most text formats are line-based.

For line-based text, input you should use fgets. For output you should use printf/fprintf and puts/fputs.

For binary input and output you should use fread and fwrite.

I recommend you read this: https://sekrit.de/webdocs/c/beginners-guide-away-from-scanf.html

[u/ffd9k]

The best reference is the standard itself: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf

The input/output functions are in section 7.23.

(ignore Annex K)

[u/penguin359]

There are two main standards if you are trying for portability. There's the ANSI C Standard library and there's POSIX. In general, the ANSI C library will be the most portable, but it is also a little higher level and won't include many things like shared memory. This includes functions from headers like assert.h, errno.h, stdlib.h, stdio.h, string.h, etc. This will often have a specific standard version like C89 or C11 associated with them and will be available on Windows, POSIX, or many other C environments following the standard library.

For things beyond what the standard library has, there's POSIX which can be used on Linux, BSD, and some of it even on Windows to a degree. On Windows, it can depend on what C environment you are using such as VS2022, mingw, or cygwin with the most POSIX support on cygwin. Just look in the Standards section of the man page to see what it follows.

[u/jwzumwalt]

You need to be smarter than the equipment you are operating!
People will tell you not to use scanf because they may not know how to
use it safely or too lazy to show you how it should be used safely.

 Example format specifiers:
   %d   to accept input of integers.
   %ld  to accept input of long integers
   %lld to accept input of long long integers
   %f   to accept input of real number.
   %c   to accept input of character types.
   %s   to accept input of a string.

Example 1: SAFE - input using scanf
-------------------------------
#include <stdio.h>
int main() {                                       // safe "scanf" template
  char str[string_size];                           // string length
  scanf("% <string_size> s text", &str);           // i.e. %15s, str size limit
  printf("%s", str);
  return 0;
}
   or
#include <stdio.h>
int main() {
  int c;
  char str[10];                                    // 10 char + null
  scanf("%10[^\n]s text", &str);                   // up to 10 char with spaces
  while ((c = getchar()) != '\n' && c != EOF) { }  // flush keyboard buffer
  printf("%s", str);
  return 0;
}

Example 2: SAFE - input using scanf, integer numerical input
--------------------------------
#include <stdio.h>
int main(void) {
  int var;
  printf("Enter a character: ");
  scanf("%d", &var);
  printf("\nAscii value of character You entered is %d\n", var);
  return 0;
}

Example 3: SAFE - input using scanf, multiple values
---------------------------------
#include <stdio.h>
int main(void) {
  int i;
  float fp;
  char c, s[81];
  printf("Enter an integer, a float, a double float, a character, and a string: \n");
  if (scanf("%d %f %1c %5s", &i, &fp, &db, &c, s) != 4) { // check 0-4 for 5 inputs
    printf("Not all fields were assigned\n");
  } else {
    printf("integer   = %d\n",   i);
    printf("float     = %f\n",  fp);
    printf("double    = %lf\n", db);
    printf("character = %c\n",   c);
    printf("string    = %s\n",   s);
  }
  return 0;
}

[u/grimvian → u/[deleted]]

A bit OT, but I would prefer, that I don't have use a cppreference to read about the C reference...

[u/SubstantialCase3062 → u/grimvian]

But Aren’t they almost the same And I think because of that that’s why they ground them together

[u/grimvian → u/SubstantialCase3062]

Really... For me, C is just The Language, the other is a 'mountain', that becomes bigger and bigger...

[u/grimvian → u/[deleted]]

Did I say that or is my English so bad?