我正在尝试编写一个程序，在执行它们之前从同一行输入(例如/bin/uname/bin/date)获取多个命令行参数，并指示该过程已成功完成。当我使用无限循环时，程序会完美地打印出每次执行，但是问题规定父进程必须在所有子进程终止后终止。尝试实现这一点只会导致一个进程完成，尽管事实上它们是一个应该允许它重复的 for 循环。任何帮助告诉我应该如何去做的人都会很棒。
我已经尝试将 for 循环移动到各种不同的位置，以及删除退出调用以尝试使其成功循环
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#define KGRN "\x1B[32m"
#define RESET "\x1B[0m"
int main(int argc,char* argv[])
{
int counter;
int status;
int COMMAND_LINE_SIZE = 64;
char command[COMMAND_LINE_SIZE];
pid_t pid;
printf("$ ");
scanf("%s", command);//read a line from user and store it in array command
printf("\n");
for(counter=0;counter<argc;counter++){
if ((pid = fork()) < 0) {
perror("forking child process failed\n");
exit(1);
}
if (pid==0){ // child
char *argv[] = {command, NULL};
execvp(argv[counter], argv);
exit(0);
}
//in parent
pid = wait(&status);
if(WIFEXITED(status) == 1)
printf(KGRN "Command %s has completed successfully\n" RESET, command);
else
printf("failure\n");
}
}
预期输出:
$ /bin/uname /bin/date /bin/ls
Linux
Command /bin/uname has completed successfully
$
Sun Sep 15 12:24:39 UTC 2019
Command /bin/date has completed successfully
$
a.out new.c q3.c trial.c
Command /bin/ls has completed successfully
当前输出:
$ /bin/ls /bin/uname
a.out new.c q3.c trial.c
Command /bin/ls has completed successfully
最佳答案
你很接近，但有很多问题，其中许多问题在问题的评论中指出:
- 您重新执行
argv[0]— 该程序 — 这预示着不妙。 - 您通常应该在 fork 子项的循环中执行子项的操作。
- 如果您希望子级并发执行，则需要在 fork 它们的循环外调用
wait()。 - 您从标准输入读取命令，即使规范说要执行命令行参数。
- 您使用从标准输入读取的数据作为已执行进程的命令名称，而不是命令行参数。
- 您有一个局部变量
argv隐藏(隐藏)main()的argv参数。因此，在counter达到 2 后，execvp()中的代码访问了argv数组的边界，并且您使用了空指针当counter为 1 时。 - 您不应该在子级执行失败后报告成功 (
exit(0);)。 - 我认为当子进程执行失败时，您应该报告哪个进程执行失败——当然是标准错误。
顺便说一下，您的示例命令行都使用了命令的完整路径，因此无需使用 execvp()。您完全可以只键入命令的名称，就像在 shell 提示符下一样，然后 execvp() 会找到该命令并运行它(请参阅我的运行示例)。
异步执行
修复这些并添加一些小的调整，并异步运行命令行参数(可能同时运行许多命令)产生如下代码:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
for (int counter = 1; counter < argc; counter++)
{
pid_t pid = fork();
if (pid < 0)
{
perror("forking child process failed\n");
exit(EXIT_FAILURE);
}
else if (pid == 0) // child
{
char *args[] = { argv[counter], NULL };
execvp(args[0], args);
fprintf(stderr, "%s: failed to execute %s: (%d) %s\n",
argv[0], argv[counter], errno, strerror(errno));
exit(EXIT_FAILURE);
}
}
int corpse;
int status;
int failed = 0;
while ((corpse = waitpid(0, &status, 0)) > 0)
{
if (WIFEXITED(status))
{
printf("Process %d exited with status %d (0x%.4X)\n",
corpse, WEXITSTATUS(status), status);
if (WEXITSTATUS(status) != 0)
failed++;
}
else if (WIFSIGNALED(status))
{
printf("Process %d was signalled %d (0x%.4X)\n",
corpse, WTERMSIG(status), status);
failed++;
}
}
return((failed == 0) ? EXIT_SUCCESS : EXIT_FAILURE);
}
failed 变量跟踪是否有任何命令失败，如果每个命令都成功，进程只会报告成功(以 0 或 EXIT_SUCCESS 退出)；否则，它将以失败指示退出(以 EXIT_FAILURE 退出，通常为 1)。
在我的 Mac 上运行时(作为从 args41.c 创建的 args41)，它产生:
$ args41 uname date ls
Sun Sep 15 07:26:58 MDT 2019
Darwin
Process 1907 exited with status 0 (0x0000)
Process 1908 exited with status 0 (0x0000)
20000-leagues-under-the-sea.txt bin maxargs.sh
LICENSE.md conn11 overlap.data
Metriseis_2012.dat conn11.c overlap47.c
README.md conn11.dSYM overlap61.c
Safe conn13 overlap73
Untracked conn13.c overlap73.c
acr.list conn13.dSYM overlap73.dSYM
acronym29.c conn17 packages
acronym43 conn17.c pseudo-json.md
acronym43.c conn17.dSYM question.md
acronym43.dSYM conn29 sll43.c
acronym47 conn29.c so-0167-2112
acronym47.c conn29.dSYM so-0167-2112.c
acronym47.dSYM doc so-0167-2112.dSYM
acronym53 dr41 so-1043-1305
acronym53.c dr41.c so-4921-8019
acronym53.dSYM dr41.dSYM so-4970-8730
acronym59 dw41 so-4971-1989
acronym59.c dw41.c so-4985-0919
acronym59.dSYM dw41.dSYM so-5102-0102
argc37 etc so-5134-1743
argc37.c gccw67 so-5225-1783
argc37.dSYM gccw67.c so-5279-4924
args41 gccw67.dSYM so-5358-5962
args41.c gccw67.o so-5394-5215
args41.dSYM get.jl.activity so-5416-6308
argv89 inc so-5424-4465.md
argv89.c lib src
argv89.dSYM makefile
Process 1909 exited with status 0 (0x0000)
$ args41 many things to do
args41: failed to execute many: (2) No such file or directory
args41: failed to execute things: (2) No such file or directory
args41: failed to execute to: (2) No such file or directory
args41: failed to execute do: (2) No such file or directory
Process 1939 exited with status 1 (0x0100)
Process 1941 exited with status 1 (0x0100)
Process 1940 exited with status 1 (0x0100)
Process 1942 exited with status 1 (0x0100)
$
显然，如果您希望进程同步运行，您应该将 waitpid() 循环放在 for 循环中。您仍然应该使用循环，因为一个进程可以继承它在模糊情况下没有 fork 的子进程。在这种情况下，您可能更愿意使用 waitpid(pid, &status, 0)；那么你不需要围绕 waitpid() 的循环。
如果您想跟踪进程名称并异步运行进程，那么父进程需要在数组中记录每个子进程的 PID，因为它们被 fork 出来，报告循环将搜索已知 child 的名单，以报告哪一个死亡。
同步执行
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
int failed = 0;
for (int counter = 1; counter < argc; counter++)
{
pid_t pid = fork();
if (pid < 0)
{
perror("forking child process failed\n");
exit(EXIT_FAILURE);
}
else if (pid == 0) // child
{
char *args[] = { argv[counter], NULL };
execvp(args[0], args);
fprintf(stderr, "%s: failed to execute %s: (%d) %s\n",
argv[0], argv[counter], errno, strerror(errno));
exit(EXIT_FAILURE);
}
else
{
int status;
if (waitpid(pid, &status, 0) < 0)
{
fprintf(stderr, "failed to wait for %s process %d: (%d) %s\n",
argv[counter], (int)pid, errno, strerror(errno));
failed++;
}
else if (WIFEXITED(status))
{
printf("Process %s exited with status %d (0x%.4X)\n",
argv[counter], WEXITSTATUS(status), status);
if (WEXITSTATUS(status) != 0)
failed++;
}
else if (WIFSIGNALED(status))
{
printf("Process %s was signalled %d (0x%.4X)\n",
argv[counter], WTERMSIG(status), status);
failed++;
}
else
{
printf("Process %s died unexpectedly (0x%.4X)\n",
argv[counter], status);
failed++;
}
}
}
return((failed == 0) ? EXIT_SUCCESS : EXIT_FAILURE);
}
示例输出(args89 从 args89.c 创建):
$ args89 date uname ls
Sun Sep 15 08:34:00 MDT 2019
Process date exited with status 0 (0x0000)
Darwin
Process uname exited with status 0 (0x0000)
20000-leagues-under-the-sea.txt argv89.c makefile
LICENSE.md argv89.dSYM maxargs.sh
Metriseis_2012.dat bin overlap.data
README.md conn11 overlap47.c
Safe conn11.c overlap61.c
Untracked conn11.dSYM overlap73
acr.list conn13 overlap73.c
acronym29.c conn13.c overlap73.dSYM
acronym43 conn13.dSYM packages
acronym43.c conn17 pseudo-json.md
acronym43.dSYM conn17.c question.md
acronym47 conn17.dSYM sll43.c
acronym47.c conn29 so-0167-2112
acronym47.dSYM conn29.c so-0167-2112.c
acronym53 conn29.dSYM so-0167-2112.dSYM
acronym53.c doc so-1043-1305
acronym53.dSYM dr41 so-4921-8019
acronym59 dr41.c so-4970-8730
acronym59.c dr41.dSYM so-4971-1989
acronym59.dSYM dw41 so-4985-0919
argc37 dw41.c so-5102-0102
argc37.c dw41.dSYM so-5134-1743
argc37.dSYM etc so-5225-1783
args41 gccw67 so-5279-4924
args41.c gccw67.c so-5358-5962
args41.dSYM gccw67.dSYM so-5394-5215
args89 gccw67.o so-5416-6308
args89.c get.jl.activity so-5424-4465.md
args89.dSYM inc src
argv89 lib
Process ls exited with status 0 (0x0000)
$
异步执行与进程名称跟踪
此变体异步运行命令，但也会跟踪属于每个 PID 的进程。请注意，它使用一个函数 (shock, horror) 来确定与刚刚死亡的 PID 对应的参数。设置数组以便于跟踪数字——未使用 PID 数组的元素 0。
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
static int find_pid(int pid, int num_pids, pid_t pids[num_pids])
{
for (int i = 1; i < num_pids; i++)
{
if (pids[i] == pid)
return i;
}
return -1;
}
int main(int argc, char *argv[])
{
pid_t pids[argc];
for (int counter = 1; counter < argc; counter++)
{
pid_t pid = fork();
if (pid < 0)
{
perror("forking child process failed\n");
exit(EXIT_FAILURE);
}
else if (pid == 0) // child
{
char *args[] = { argv[counter], NULL };
execvp(args[0], args);
fprintf(stderr, "%s: failed to execute %s: (%d) %s\n",
argv[0], argv[counter], errno, strerror(errno));
exit(EXIT_FAILURE);
}
else
pids[counter] = pid;
}
int corpse;
int status;
int failed = 0;
while ((corpse = waitpid(0, &status, 0)) > 0)
{
int index = find_pid(corpse, argc, pids);
if (index < 0)
{
fprintf(stderr, "Unrecognized PID %d exited with status 0x%.4X\n",
corpse, status);
failed++;
}
else if (WIFEXITED(status))
{
printf("Process %s (PID %d) exited with status %d (0x%.4X)\n",
argv[index], corpse, WEXITSTATUS(status), status);
if (WEXITSTATUS(status) != 0)
failed++;
}
else if (WIFSIGNALED(status))
{
printf("Process %s (PID %d) was signalled %d (0x%.4X)\n",
argv[index], corpse, WTERMSIG(status), status);
failed++;
}
else
{
printf("Process %s (PID %d) died from indeterminate causes (0x%.4X)\n",
argv[index], corpse, status);
failed++;
}
}
return((failed == 0) ? EXIT_SUCCESS : EXIT_FAILURE);
}
运行示例(args79 从 args79.c 创建):
$ args79 uname date pwd
/Users/jleffler/soq
Process pwd (PID 2105) exited with status 0 (0x0000)
Darwin
Sun Sep 15 09:04:37 MDT 2019
Process uname (PID 2103) exited with status 0 (0x0000)
Process date (PID 2104) exited with status 0 (0x0000)
$
关于c - 如何让 execvp 函数执行每个命令行参数？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/57944117/