test program for pread and pwrite

pwrite_pread.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>
#include <fcntl.h>
#include <unistd.h>

#define FILENAME "pwrite_pread.dat"

void test_pwrite()
{
        int fd;
        char buf[10];

        if((fd = open(FILENAME, O_RDWR|O_CREAT, 0660)) == -1)
                err(1, "open");

        if(write(fd, "987", 3) != 3)
                err(1, "write");

        if(pwrite(fd, "789", 3, 7) != 3)
                err(1, "pwrite");

        if(write(fd, "654", 3) != 3)
                err(1, "write");

        if(pwrite(fd, "456", 3, 4) != 3)
                err(1, "pwrite");

        if(write(fd, "3210", 4) != 4)
                err(1, "write");

        if(pwrite(fd, "0123", 4, 0) != 4)
                err(1, "pwrite");

        if(close(fd) == -1)
                err(1, "close");

        if((fd = open(FILENAME, O_RDONLY)) == -1)
                err(1, "open");

        if(read(fd, buf, 10) != 10)
                err(1, "read");

        if(strncmp(buf, "0123453210", 10) != 0)
                err(1, "strncmp");

        if(close(fd) == -1)
                err(1, "close");
}

void test_pread()
{
        int fd;
        char buf[10];

        if((fd = open(FILENAME, O_RDONLY)) == -1)
                err(1, "open");

        if(read(fd, buf, 3) != 3)
                err(1, "read");
        if(strncmp(buf, "012", 3) != 0)
                err(1, "strncmp");

        if(pread(fd, buf, 3, 7) != 3)
                err(1, "pread");
        if(strncmp(buf, "210", 3) != 0)
                err(1, "strncmp");

        if(read(fd, buf, 3) != 3)
                err(1, "read");
        if(strncmp(buf, "345", 3) != 0)
                err(1, "strncmp");

        if(pread(fd, buf, 3, 4) != 3)
                err(1, "pread");
        if(strncmp(buf, "453", 3) != 0)
                err(1, "strncmp");

        if(read(fd, buf, 4) != 4)
                err(1, "read");
        if(strncmp(buf, "3210", 4) != 0)
                err(1, "strncmp");

        if(pread(fd, buf, 4, 0) != 4)
                err(1, "pread");
        if(strncmp(buf, "0123", 4) != 0)
                err(1, "strncmp");

        if(read(fd, buf, 1) != 0)
                err(1, "read");

        if(close(fd) == -1)
                err(1, "close");
}

int main(int argc, char *argv[])
{
        test_pwrite();
        test_pread();
}