Random access with fseek(). - C File

C examples for File:File Read

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Description

Random access with fseek().

Demo Code

#include <stdlib.h>
#include <stdio.h>

#define MAX 50//from w ww .ja  v a 2s  . c o  m

int main( void )
{
    FILE *fp;
    int data, count, array[MAX];
    long offset;

    for (count = 0; count < MAX; count++)
        array[count] = count * 10;

    /* Open a binary file for writing. */

    if ( (fp = fopen("RANDOM.DAT", "wb")) == NULL)
    {
        fprintf(stderr, "\nError opening file.");
        exit(1);
    }

    /* Write the array to the file, then close it. */

    if ( (fwrite(array, sizeof(int), MAX, fp)) != MAX)
    {
        fprintf(stderr, "\nError writing data to file.");
        exit(1);
    }

    fclose(fp);

    /* Open the file for reading. */

    if ( (fp = fopen("RANDOM.DAT", "rb")) == NULL)
    {
        fprintf(stderr, "\nError opening file.");
        exit(1);
    }

    while (1)
    {
        printf("\nEnter element to read, 0-%d, -1 to quit: ",MAX-1);
        scanf("%ld", &offset);

        if (offset < 0)
            break;
        else if (offset > MAX-1)
            continue;

        /* Move the position indicator to the specified element. */

        if ( (fseek(fp, (offset*sizeof(int)), SEEK_SET)) != 0)
        {
            fprintf(stderr, "\nError using fseek().");
            exit(1);
        }

        /* Read in a single integer. */

        fread(&data, sizeof(int), 1, fp);

        printf("\nElement %ld has value %d.", offset, data);
    }

    fclose(fp);
    return 0;
}

Result


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