[英]Linux C Shell, segmentation fault thrown by child process
我一直在嘗試為作業寫一個C,說要創建一個C shell。 一個要求是所有命令應從子進程執行。 問題似乎是我的子進程死得太早了,而我從沒有真正執行命令的那部分代碼。 我的代碼:
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
}
}
輸出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
我幾天前才剛開始學習C,但是我用google搜索了C中的分段錯誤,看來我在取消引用未初始化的指針,還是試圖訪問釋放的內存。 所以我嘗試注釋掉
free(cmdStr);
行,然后輸出如下所示:
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
我也嘗試在parseCommand.h的while循環中移動print語句,但是輸出似乎也沒有改變。 我已經問過幾個C ++教授,但他們都無法指出錯誤。 這里有人可以給我一些有關我的錯誤的提示嗎?
提前非常感謝您!
有幾個問題-
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 *
就這樣-
char *cmdStr =malloc(40);
fgets(cmdStr, 40, stdin);
2.也在這里-
char *cmd = parseCommand(&cmdStr);//split user input by space
printf("cmd: %s", &cmd); //cmd is already a char * don't pass its address
這樣寫-
printf("cmd: %s", cmd);
3.在您的函數char *parseCommand(char str[])
當您計算元素數時-
size_t n = sizeof(str) / sizeof(str[0]);
這不會按預期工作。 因此,在main
計算n
,然后將其傳遞給您的函數
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