FIFO写管道fd = open(FIFO_SERVER, O_WRONLY | O_NONBLOCK,0);出现错误

Question

这是代码段

这是出现的错误，提示FIFO_SERVER没有定义

请求帮助！！！

Answer 1

因为系统默认的fifo权限是000, 所以你需要先修改权限再open
完整的代码如下

read

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

#define FIFO_SERVER "/tmp/myfifo"

main(int argc, char** argv) {
    char buf_r[100];
    int fd;
    int nread;
    if ((mkfifo(FIFO_SERVER, O_CREAT | O_EXCL |O_RDWR) < 0) && (errno != EEXIST))
    {
        perror("can not creat fifoserver");
        exit(1);
    }

    char cmd[100];
    sprintf(cmd, "chmod 704 %s", FIFO_SERVER);
    system(cmd);

    printf("preparing for reading bytes...\n");
    memset(buf_r, 0, sizeof(buf_r));
    fd = open(FIFO_SERVER, O_RDONLY | O_NONBLOCK, 0);
    if (fd == -1) {
        perror("open");
        exit(1);
    }
    while (1)
    {
        memset(buf_r, 0, sizeof(buf_r));
        if ((nread = read(fd, buf_r, 100)) == -1) {
            if (errno == EAGAIN)
                printf("no data yet\n");
        }
        printf("read %s from FIFO\n", buf_r);
        sleep(1);
    }
//    pause();
    close(fd);
    unlink(FIFO_SERVER);
}

write

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

#define FIFO_SERVER "/tmp/myfifo"

int main(int argc, char** argv)
{
    int fd;
    char w_buf[100];
    int nwrite;

    fd = open(FIFO_SERVER, O_WRONLY | O_NONBLOCK,0);
    if (fd == -1)
    {
        perror("open error;no reading process");
        exit(1);
    }
    if (argc == 1)
    {
        printf("please send somenthing\n");
        exit(1);
    }
    strcpy(w_buf, argv[1]);
    if ((nwrite = write(fd, w_buf, 100)) == -1)
    {
        if (errno == EAGAIN)
            printf("the fifo has not been read yet.Please try later\n");
    }
    else
        printf("write %s to the fifo\n", w_buf);
    close(fd);
    return 0;
}

运行

先运行reader, 再运行writer

reader

harriszh Fri 1:03@ ~/trunk/cpp/fifo3$ ./read
preparing for reading bytes...
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read abc from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read abc from FIFO
read  from FIFO
read  from FIFO
read  from FIFO
read  from FIFO

writer

harriszh Fri 1:03@ ~/trunk/cpp/fifo3$ ./write abc
write abc to the fifo
harriszh Fri 1:03@ ~/trunk/cpp/fifo3$ ./write "abc"
write abc to the fifo

Answer 2

open函数
摘自linux程序设计第三章
FIFO
摘自linux程序设计第十三章
你这一段代码应该是在别的地方有FIFO_SERVER(FIFO文件的路径)的定义

------补充
就你这边的代码看你如果#define FIFO_SERVER "/tmp/myfifo" 在这个目录下你有一个myfifo 的管道文件
错误原因是core dump 应该是你在这个地方没有这个文件吧.

Answer 3

现在上面的问题解决了，但是没有出现预期的结果

#include<sys/types.h>
#include<sys/stat.h>
#include<errno.h>
#include<fcntl.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define FIFO "/tmp/myfifo"
main(int argc, char** argv)
{
    int fd;
    char w_buf[100];
    int nwrite;
    if (fd == -1)
        if (errno == ENXIO)
            printf("open errop;no reading process\n");
    fd = open(FIFO_SERVER, O_WRONLY | O_NONBLOCK,0);
    if (argc == 1)
        printf("please send somenthing\n");
    strcpy(w_buf, argv[1]);
    if ((nwrite = write(fd, w_buf, 100)) == -1)
    {
        if (errno == EAGAIN)
            printf("the fifo has not been read yet.Please try later\n");
    }
    else
        printf("write %s to the fifo\n", w_buf);
}
这是完整的代码？不知道哪里出现了错误
在打开终端进行读操作的时候显示

下面是读的代码：

#include<sys/types.h>
#include<sys/stat.h>
#include<errno.h>
#include<fcntl.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define FIFO_SERVER "/tmp/myfifo"
main(int argc, char** argv) {
    char buf_r[100];
    int fd;
    int nread;
    if ((mkfifo(FIFO_SERVER, O_CREAT | O_EXCL) < 0) && (errno != EEXIST))
        printf("can not creat fifoserver\n");
    printf("preparing for reading bytes...\n");
    memset(buf_r, 0, sizeof(buf_r));
    fd = open(FIFO_SERVER, O_RDONLY | O_NONBLOCK, 0);
    if (fd == -1) {
        perror("open");
        exit(1);
    }
    while (1)
    {
        memset(buf_r, 0, sizeof(buf_r));
        if ((nread = read(fd, buf_r, 100)) == -1) {
            if (errno == EAGAIN)
                printf("no data yet\n");
        }
        printf("read %s from FIFO\n", buf_r);
        sleep(1);
    }
    pause();
    unlink(FIFO_SERVER);
}

这是一个终端执行第一段代码，写没有错误提示