fseek

 

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>
int fseek( FILE *stream, long offset, int origin );

Sets the file position indicator for the file stream stream to the value pointed to by offset. This function can be used to set the indicator beyond the actual end of the file, however, negative position values are not accepted.

Parameters

stream	-	file stream to modify
offset	-	number of characters to shift the position relative to origin
origin	-	position to which offset is added. It can have one of the following values: SEEK_SET, SEEK_CUR, SEEK_END

Return value

​0​ upon success, nonzero value otherwise. Associated EOF flag is cleared for the stream and the effect of any ungetc is undone.

Notes

For text streams, the only valid values of offset are ​0​ (applicable to any origin) and a value returned by an earlier call to ftell (only applicable to SEEK_SET).

Example

fseek 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");
 
    /* Set the file position indicator in front of third f-p value. */
    if (fseek(fp,sizeof(double)*2L,SEEK_SET) != 0)
    {
       if (ferror(fp))
       {
          perror("fseek()");
          fprintf(stderr,"fseek() failed in file %s at line # %d\n", __FILE__,__LINE__-5);
          exit(EXIT_FAILURE);
       }
    }
 
    int ret_code = fread(B,sizeof(double),1,fp);   /* read one f-p value  */
    printf("%.1f\n", B[0]);                        /* print one f-p value */
 
    fclose(fp);
    return EXIT_SUCCESS;
}

Output:

3.0

See also

fsetpos	moves the file position indicator to a specific location in a file (function)
fgetpos	gets the file position indicator (function)
ftell	returns the current file position indicator (function)
rewind	moves the file position indicator to the beginning in a file (function)
C++ documentation for fseek