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# fsetpos

From cppreference.com
< c‎ | io

Defined in header `<stdio.h>` |  |
int fsetpos( FILE *stream, const fpos_t *pos ); |  |

Sets the file position indicator and the multibyte parsing state (if any) for the file stream `stream` according to the value pointed to by `pos`.

Besides establishing new parse state and position, a call to this function undoes the effects of ungetc and clears the end-of-file state, if it is set.

If a read or write error occurs, the error indicator (ferror) for the stream is set.

### [edit] Parameters

stream | - | file stream to modify
pos | - | pointer to a fpos_t object to use as new value of file position indicator

### [edit] Return value

​0​ upon success, nonzero value otherwise.

### [edit] Notes

After seeking to a non-end position in a wide stream, the next call to any output function may render the remainder of the file undefined, e.g. by outputting a multibyte sequence of a different length.

### [edit] Example

fsetpos 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");
        fpos_t pos;
        if (fgetpos(fp,&pos) != 0)      /* current position: start of file */
        {
           perror("fgetpos()");
           fprintf(stderr,"fgetpos() failed in file %s at line # %d\n", __FILE__,__LINE__-3);
           exit(EXIT_FAILURE);
        }

        int ret_code = fread(B,sizeof(double),1,fp);   /* read one f-p value */
        /* current position: after reading one f-p value */
        printf("%.1f\n", B[0]);   /* print one f-p value */

        if (fsetpos(fp,&pos) != 0)   /* reset current position to start of file */
        {
           if (ferror(fp))
           {
              perror("fsetpos()");
              fprintf(stderr,"fsetpos() failed in file %s at line # %d\n", __FILE__,__LINE__-5);
              exit(EXIT_FAILURE);
           }
        }

        ret_code = fread(B,sizeof(double),1,fp);   /* reread first f-p value */
        printf("%.1f\n", B[0]);                    /* print one f-p value    */
        fclose(fp);

        return EXIT_SUCCESS;
    }

Output:

    1.0
    1.0

### [edit] References

- C11 standard (ISO/IEC 9899:2011):

  - 7.21.9.3 The fsetpos function (p: 337)

- C99 standard (ISO/IEC 9899:1999):

  - 7.19.9.3 The fsetpos function (p: 303)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.9.9.3 The fsetpos function

### [edit] See also

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

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