Linux System Programming 学习笔记(四) 高级I/O

#include <sys/uio.h>

struct iovec {
       void *iov_base;    /* pointer to start of buffer */
       size_t iov_len;    /* size of buffer in bytes */
};

/* The readv() function reads count segments from the file descriptor fd into the buffers described by iov */
ssize_t readv (int fd, const struct iovec *iov, int count);

/* The writev() function writes at most count segments from the buffers described by iov into the file descriptor fd */
ssize_t writev (int fd, const struct iovec *iov, int count);

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <sys/uio.h>

int main(int argc, char* argv[])
{
    struct iovec iov[3];
    char* buf[] = {
        "The term buccaneer comes from the word boucan.\n",
        "A boucan is a wooden frame used for cooking meat.\n",
        "Buccaneer is the West Indies name for a pirate.\n" };

    int fd = open("wel.txt", O_WRONLY | O_CREAT | O_TRUNC);
    if (fd == -1) {
        fprintf(stderr, "open error\n");
        return 1;
    }

    /* fill out three iovec structures */
    for (int i = 0; i < 3; ++i) {
        iov[i].iov_base = buf[i];
        iov[i].iov_len  = strlen(buf[i]) + 1;
    }

    /* with a single call, write them out all */
    ssize_t nwrite = writev(fd, iov, 3);
    if (nwrite == -1) {
        fprintf(stderr, "writev error\n");
        return 1;
    }
    fprintf(stdout, "wrote %d bytes\n", nwrite);
    if (close(fd)) {
        fprintf(stdout, "close error\n");
        return 1;
    }

    return 0;
}

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/uio.h>
#include <sys/stat.h>

int main(int argc, char* argv[])
{
    char foo[48], bar[51], baz[49];
    struct iovec iov[3];
    int fd = open("wel.txt", O_RDONLY);
    if (fd == -1) {
        fprintf(stderr, "open error\n");
        return 1;
    }

    /* set up our iovec structures */
    iov[0].iov_base = foo;
    iov[0].iov_len =  sizeof(foo);
    iov[1].iov_base = bar;
    iov[1].iov_len =  sizeof(bar);
    iov[2].iov_base = baz;
    iov[2].iov_len =  sizeof(baz);

    /* read into the structures with a single call */
    ssize_t nread = readv(fd, iov, 3);
    if (nread == -1) {
        fprintf(stderr, "readv error\n");
        return 1;
    }

    for (int i = 0; i < 3; ++i) {
        fprintf(stdout, "%d: %s", i, (char*)iov[i].iov_base);
    }
    if (close(fd)) {
        fprintf(stderr, "close error\n");
        return 1;
    }

    return 0;
}

#include <unistd.h>
#include <sys/uio.h>

ssize_t my_writev(int fd, const struct iovec* iov, int count)
{
    ssize_t ret = 0;
    for (int i = 0; i < count; ++i) {
        ssize_t nr = write(fd, iov[i].iov_base, iov[i].iov_len);
        if (nr == -1) {
            if (errno == EINTR)
                continue;
            ret -= 1;
            break;
        }
        ret += nr;
    }
    return nr;
}