您的管道以阻塞模式打开,您没有做任何更改,这可能是您想要的。
但是,由于您要做的第一件事是请求管道上等待的数据大小,然后盲目地跳入读取那么多字节(由于父级尚未写入任何内容,因此代码执行时该字节很可能为零) 你没有阻止,而是离开,因为你什么都没要求。
有很多方法可以做到这一点,包括选择循环。如果您希望在数据可用之前阻止读取,则在单个字节上执行此操作,然后填写剩余数据。
这绝不是如何正确执行此操作的示例,但它是一个简短示例,说明如何等待单个字节,请求管道的读取大小以获取其余数据,读取它,以及继续此操作,直到管道没有剩余数据并且父级关闭其末端:
我希望你觉得这对你有帮助。
#include <stdio.h>
#include <unistd.h>
#include <sys/ioctl.h>
int main()
{
int pid = 0;
// create pipe pair
int fd[2];
pipe(fd);
pid = fork();
if (pid == 0)
{
// child side
char *buff = NULL;
char byte = 0;
int count = 0;
// close write side. don't need it.
close(fd[1]);
// read at least one byte from the pipe.
while (read(fd[0], &byte, 1) == 1)
{
if (ioctl(fd[0], FIONREAD, &count) != -1)
{
fprintf(stdout,"Child: count = %d\n",count);
// allocate space for the byte we just read + the rest
// of whatever is on the pipe.
buff = malloc(count+1);
buff[0] = byte;
if (read(fd[0], buff+1, count) == count)
fprintf(stdout,"Child: received \"%s\"\n", buff);
free(buff);
}
else
{ // could not read in-size
perror("Failed to read input size.");
}
}
// close our side
close(fd[0]);
fprintf(stdout,"Child: Shutting down.\n");
}
else
{ // close read size. don't need it.
const char msg1[] = "Message From Parent";
const char msg2[] = "Another Message From Parent";
close(fd[0]);
sleep(5); // simulate process wait
fprintf(stdout, "Parent: sending \"%s\"\n", msg1);
write(fd[1], msg1, sizeof(msg1));
sleep(5); // simulate process wait
fprintf(stdout, "Parent: sending \"%s\"\n", msg2);
write(fd[1], msg2, sizeof(msg2));
close(fd[1]);
fprintf(stdout,"Parent: Shutting down.\n");
}
return 0;
}
输出
Parent: sending "Message From Parent"
Child: count = 19
Child: received "Message From Parent"
Parent: sending "Another Message From Parent"
Parent: Shutting down.
Child: count = 27
Child: received "Another Message From Parent"
Child: Shutting down.