fopen - C stdio.h

C examples for stdio.h:fopen

  1. HOME
  2. C
  3. stdio.h
  4. fopen

Type

function

From 


<cstdio>
<stdio.h>

Description

Open file with filename and open mode

Prototype 

FILE * fopen ( const char * filename, const char * mode );

Parameters

ParameterDescription
filename C string containing the file name .
mode C string containing a file access mode.

mode value can be:

Value Action Description
"r"read Open file for reading. The file must exist.
"w"write Create an empty file for writing. If the file already exists, empty the existing file.
"a"appendOpen file for appending. The file is created if it does not exist.
"r+" read/update Open a file both for input and output. The file must exist.
"w+" write/update Create an empty file and open it both for input and output. If the file already exists, empty the existing file.
"a+" append/update Open a file both for input and output, append to the end of the file. The file is created if it does not exist.

With the mode specifiers above the file is open as a text file.

In order to open a file as a binary file, a "b" character has to be included in the mode string.

This additional "b" character can either be appended at the end of the string.

It makes the following compound modes: "rb", "wb", "ab", "r+b", "w+b", "a+b") or ("rb+", "wb+", "ab+").

Legal Values for the mode Parameter of fopen( ) to work on text or binary file

Mode Meaning
"r" Open text file for reading
"w"Create a text file for writing
"a" Append to text file
"rb" Open binary file for reading
"wb" Create binary file for writing
"ab" Append to a binary file
"r+" Open text file for read/write
"w+" Create text file for read/write
"a+" Open text file for read/write
"rb+" or "r+b" Open binary file for read/write
"wb+" or "w+b" Create binary file for read/write
"ab+" or "a+b" Open binary file for read/write

Return Value

On success, the function returns a pointer to a FILE object.

Otherwise, a null pointer is returned.

The correct method of opening a file is illustrated by this code fragment: 

FILE *fp;

if ((fp = fopen("test", "w"))==NULL) {
  printf("Cannot open file.\n");
  exit(1);
}

This fragment opens a file called TEST for binary read/write operations: 

FILE *fp;

if((fp=fopen("test", "rb+"))==NULL) {
  printf("Cannot open file.\n");
  exit(1);
}

Demo Code


#include <stdio.h>
int main ()/*from   ww w.  ja v  a  2s  .c o m*/
{
  FILE * pFile;
  pFile = fopen ("main.cpp","w");
  if (pFile==NULL){
      perror ("Error opening file");
      return -1;
  }

  fputs ("fopen example",pFile);
  fclose (pFile);

  return 0;
}

Related Tutorials