我必须创建 2 个子进程并将数据从父进程发送到两个子进程,所以我使用了pipe
.
如果我只使用 1 个子进程和 1 个管道,那么一切都可以与fdopen
,fscanf
和完美配合fprintf
。此外,如果我创建 2 个管道并将数据发送到单个进程,仍然可以正常工作。
但是,如果我创建第二个进程并尝试从第二个进程中读取pipe
,则什么也不会发生。
例如:
int main() {
pid_t pid1, pid2;
int a[2];
pipe(a);
pid1 = fork();
if(pid1 == 0) {
char x,y;
FILE *stream;
stream = fdopen(a[0],"r");
fscanf(stream,"%c",&x);
printf("%c\n", x);
close(a[1]);
close(a[0]);
} else {
int b[2];
pipe(b);
pid2 = fork();
FILE *stream1, *stream2;
close(a[0]);
close(b[0]);
stream1 = fdopen(a[1],"w");
stream2 = fdopen(b[1],"w");
fprintf(stream1, "yo bella zio\n");
fprintf(stream2, "como estas\n");
fflush(stream1);
fflush(stream2);
close(a[1]);
close(b[1]);
waitpid (pid1, NULL, 0);
waitpid (pid2, NULL, 0);
if (pid2 == 0) {
FILE *stream;
close(b[1]);
close(a[1]);
close(a[0]);
stream = fdopen(b[0],"r");
fscanf(stream,"%c",&x);
printf("%c\n", x);
} else {
}
}
}
我真的尝试了所有的组合。一起声明所有管道,关闭或不关闭管道。一切,但一无所有。
此代码修复了我的评论中发现的问题和一些杂散问题。
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int main(void)
{
pid_t pid1, pid2;
int a[2];
int b[2];
pipe(a);
pid1 = fork();
if (pid1 < 0)
{
fprintf(stderr, "failed to fork child 1 (%d: %s)\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
else if (pid1 == 0)
{
close(a[1]); // Must be closed before the loop
FILE *stream = fdopen(a[0], "r");
if (stream == NULL)
{
fprintf(stderr, "failed to create stream for reading (%d: %s)\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
int c;
while ((c = getc(stream)) != EOF)
putchar(c);
//char x;
//fscanf(stream, "%c", &x);
//printf("%c\n", x);
//close(a[0]); -- Bad idea once you've used fdopen() on the descriptor
printf("Child 1 done\n");
exit(0);
}
else
{
pipe(b);
pid2 = fork();
if (pid2 < 0)
{
fprintf(stderr, "failed to fork child 2 (%d: %s)\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
else if (pid2 == 0)
{
close(b[1]);
close(a[1]);
close(a[0]);
FILE *stream = fdopen(b[0], "r");
if (stream == NULL)
{
fprintf(stderr, "failed to create stream for reading (%d: %s)\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
int c;
while ((c = getc(stream)) != EOF)
putchar(c);
//char x;
//fscanf(stream, "%c", &x);
//printf("%c\n", x);
printf("Child 2 done\n");
exit(0);
}
}
close(a[0]);
close(b[0]);
FILE *stream1 = fdopen(a[1], "w");
if (stream1 == NULL)
{
fprintf(stderr, "failed to create stream for writing (%d: %s)\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
FILE *stream2 = fdopen(b[1], "w");
if (stream2 == NULL)
{
fprintf(stderr, "failed to create stream for writing (%d: %s)\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(stream1, "yo bella zio\n");
fprintf(stream2, "como estas\n");
fflush(stream1); // Not necessary because fclose flushes the stream
fflush(stream2); // Not necessary because fclose flushes the stream
fclose(stream1); // Necessary because child won't get EOF until this is closed
fclose(stream2); // Necessary because child won't get EOF until this is closed
//close(a[1]); -- bad idea once you've used fdopen() on the descriptor
//close(b[1]); -- bad idea once you've used fdopen() on the descriptor
waitpid(pid1, NULL, 0);
waitpid(pid2, NULL, 0);
printf("All done!\n");
return 0;
}
请注意,我更改了子进程,以便 (a) 它们在代码块中显式退出,并且 (b) 将它们的主体放入一个循环中,以便打印所有发送的数据。这需要我移动close(a[1])
第一个孩子;否则,循环不会终止,因为 o/s 看到 child 1 已打开描述符以进行写入。
在运行 macOS 10.13.6 High Sierra(GCC 8.2.0 作为编译器)的 Mac 上执行时,我得到输出:
yo bella zio
Child 1 done
como estas
Child 2 done
All done!
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