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重定向輸入與輸出
大多數的IDE環境都具備這樣一種功能，加載編譯器編譯好程序并執行，執行結果顯示于IDE環境中的結果信息窗口，那么它是如何捕獲程序運行結果的呢？其實簡單地用dup/dup2重定位輸出并通過管道獲取該輸出就可以達到這種效果。 #include stdio.h #include unistd
大多數的IDE環境都具備這樣一種功能，加載編譯器編譯好程序并執行，執行結果顯示于IDE環境中的結果信息窗口，那么它是如何捕獲程序運行結果的呢？其實簡單地用dup/dup2重定位輸出并通過管道獲取該輸出就可以達到這種效果。#include <stdio.h> #include <unistd.h> #include <string.h> #include <errno.h> #include <sys/types.h> int main(int argc, char **argv)
{
int fd[2];
pid_t childpid;
if (pipe(fd) == -1)
{
printf("%s: %d -- Create pipe error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
childpid = fork();
if (childpid == -1)
{
printf("%s: %d -- fork error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
if (childpid == 0)
{
close(fd[0]);
if (dup2(fd[1], STDOUT_FILENO) == -1)
{
printf("%s: %d -- dup2 error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
if (execlp("ls", "ls", "/", NULL) == -1)
{
printf("%s: %d -- execlp error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
exit(0);
}
else { char buff[4096];
close(fd[1]);
memset(buff, sizeof(buff), 0);
printf("read %d bytes\n", read(fd[0], buff, sizeof(buff)));
printf("output: %s\n", buff);
exit(0);
}
}
以下代碼則相反，重定向輸入：
#include <stdio.h> #include <unistd.h> #include <string.h> #include <errno.h> #include <sys/types.h> #include <sys/wait.h> int main(int argc, char **argv)
{
int fd[2];
pid_t childpid;
if (pipe(fd) == -1)
{
printf("%s: %d -- Create pipe error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
childpid = fork();
if (childpid == -1)
{
printf("%s: %d -- fork error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
if (childpid == 0)
{
close(fd[1]);
if (dup2(fd[0], STDIN_FILENO) == -1)
{
printf("%s: %d -- dup2 error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
if (execlp("xargs", "xargs", "ls", NULL) == -1)
{
printf("%s: %d -- execlp error: %s\n", __FILE__, __LINE__, strerror(errno));
exit(errno);
}
exit(0);
}
else { int status;
close(fd[0]);
write(fd[1], "/", 1);
printf("waitpid result: %d\n", waitpid(childpid, &status, WNOHANG));
printf("status value: %d\n", status);
if (WIFEXITED(status))
printf("child process was terminated normally by calling exit or _exit\n");
else if (WEXITSTATUS(status))
printf("returns the exit status of the child by exit or _exit\n");
else if (WIFSIGNALED(status))
printf("child process was terminated by a signal\n");
else if (WTERMSIG(status))
printf("returns the number of the signal that caused the child process to terminate\n");
else if (WCOREDUMP(status))
printf("child produced a core dump\n");
else if (WIFSTOPPED(status))
printf("child process was stopped by delivery of a signal\n");
else if (WSTOPSIG(status))
printf("retuns the number of the signal which caused the child to stop\n");
else if (WIFCONTINUED(status))
printf("child process was resumed by delivery of SIGCONT\n");
exit(0);
}
}
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