我一直在尝试选择 C 语言来完成要求创建 C shell 的家庭作业。一个要求是所有命令都应该从子进程中执行。问题似乎是我的子进程死得太早了,而且我从来没有接触到实际执行命令的代码部分。我的代码:
parseCommand.h
char *parseCommand(char str[]) {
char * token;
//get size of the input array. divide memory amount allocated to array by the size of the 1st element (which should be representative of other elements)
size_t n = sizeof(str) / sizeof(str[0]);
char *args = malloc(n);
printf("Splitting string \"%s\" into tokens:\n", str);
token = strtok(str, " \n");
int i = 0;
while (token != NULL) {
printf(":: %s\n", token);
args[i++] = token;
token = strtok(NULL, " \n");
}
printf("after while loop");
args[i]=(char *) 0;
return args;
}
main.c
//I probably don't need all these
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>
//Custom Libraries
#include "parseCommand.h"
char *parseCommand(char str[]);
int main() {
char path[10] = "/bin/";//path to bash scripts
int should_run = 1;
while (should_run) {
printf("yazan_shell>> ");
fflush(stdout); //force the prompt to the output immediately
char *cmdStr = (char *)malloc(40); //allocate space for array
fgets(&cmdStr, 40, stdin); //save user input to cmdStr
pid_t pid = fork(); //create
if (pid == 0) {
printf("==> Child received: %s command. Executing...\n", &cmdStr);
char *cmd = parseCommand(&cmdStr);//split user input by space
printf("cmd: %s", &cmd);
execvp(strcat(path, cmd[0]), cmd);//excecute the input cmd
} else {
int returnStatus;
waitpid(pid, &returnStatus, 0); //parent waits for child process
printf("==> Parent is silent!! PID: %d\n", pid);
should_run = 0;
}
free(cmdStr); //deallocate cmdStr
}
}
输出 1
yazan_shell>> ls -l
==> Child received: ls -l
command. Executing...
Splitting string "ls -l
" into tokens:
:: ls
:: -l
==> Parent is silent!! PID: 5500
RUN FINISHED; Segmentation fault; core dumped; real time: 3s; user: 0ms; system: 0ms
我几天前才开始学习 C,但我用谷歌搜索了 C 中的段错误,看来我不是在取消引用未初始化的指针,就是在尝试访问已释放的内存。所以我试着注释掉
free(cmdStr);
行,然后输出如下所示:
yazan_shell>> ls -l
==> Child received: ls -l
command. Executing...
Splitting string "ls -l
" into tokens:
:: ls
:: -l
==> Parent is silent!! PID: 5601
RUN FINISHED; exit value 33; real time: 1s; user: 0ms; system: 0ms
我还尝试在 parseCommand.h 的 while 循环中移动 print 语句,但输出似乎也没有改变。我问过几位有空的 C++ 教授,但他们都无法查明错误。这里有人能给我一些关于我的错误的指示(呵呵)吗?
非常感谢您!
最佳答案
有几个问题-
1. 在 main
-
char *cmdStr = (char *)malloc(40); // don't cast it
fgets(&cmdStr, 40, stdin); // don't pass address of cmdStr it is already a char *
就这样就好了-
char *cmdStr =malloc(40);
fgets(cmdStr, 40, stdin);
2.也在这里-
char *cmd = parseCommand(&cmdStr);//split user input by space
printf("cmd: %s", &cmd); //cmd is already a char * don't pass its address
这样写——
printf("cmd: %s", cmd);
3. 在您的函数 char *parseCommand(char str[])
中计算元素数量时 -
size_t n = sizeof(str) / sizeof(str[0]);
这不会按预期工作。所以在main
中计算n
,然后将它传递给你的函数
关于c - Linux C Shell,子进程抛出段错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/33188215/