fread

 

C

Language

Standard Library

Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

File input/output

Functions
File access
fopen freopen fclose fflush	fwide setbuf setvbuf
Direct input/output
fread
fwrite
Unformatted input/output
fgetc fgets fputc fputs getchar gets putchar puts ungetc	fgetwc fgetws fputwc fputws getwchar putwchar ungetwc
Formatted input/output
scanffscanfsscanf vscanfvfscanfvsscanf (C99)(C99)(C99) printffprintfsprintfsnprintf (C99) vprintfvfprintfvsprintfvsnprintf (C99)	wscanffwscanfswscanf vwscanfvfwscanfvswscanf (C99)(C99)(C99) wprintffwprintfswprintf vwprintfvfwprintfvswprintf
File positioning
ftell
fgetpos
fseek
fsetpos
rewind
Error handling
clearerr
feof
ferror
perror
Operations on files
remove
rename
tmpfile
tmpnam

 

Defined in header <stdio.h>
size_t fread( void          *buffer, size_t size, size_t count,               FILE          *stream );		(until C99)
size_t fread( void *restrict buffer, size_t size, size_t count,               FILE *restrict stream );		(since C99)

Reads specified number of objects in the array buffer from the given input stream stream. Objects are not interpreted in any way.

Parameters

buffer	-	pointer to the array where the read objects are stored
size	-	size of each object in bytes
count	-	the number of the objects to be read
stream	-	the stream to read

Return value

The number of objects read successfully.

Example

fread with error checking

Run this code

#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    /* Prepare an array of f-p values. */
    #define SIZE 5
    double A[SIZE] = {1.,2.,3.,4.,5.};
    /* Write array to a file. */
    FILE * fp = fopen("test.bin", "wb");
    fwrite(A,sizeof(double),SIZE,fp);
    fclose (fp);
 
    /* Read the f-p values into array B. */
    double B[SIZE];
    fp = fopen("test.bin","rb");
    int ret_code = fread(B,sizeof(double),SIZE,fp);
    if (ret_code < SIZE)
    {
       if (feof(fp))
          printf("EOF reached\n");
       else if (ferror(fp))
            {
              perror("fread()");
              fprintf(stderr,"fread() failed in file %s at line # %d\n", __FILE__,__LINE__-8);
              exit(EXIT_FAILURE);
            }
    }
    printf("%.1f\n", B[4]);   /* print one f-p value */
 
    return EXIT_SUCCESS; 
}

Output:

5.0

See also

scanffscanfsscanf	reads formatted input from stdin, a file stream or a buffer (function)
fgets	gets a character string from a file stream (function)
fwrite	writes to a file (function)
C++ documentation for fread