<分区>
我想理解这段代码，特别是 parse_args。这段代码就像运行 pwd cat 等基本 linux 命令的简单 shell。我想了解 parse_args 的工作原理。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#define BUFFER_SIZE 1<<16
#define ARR_SIZE 1<<16
void parse_args(char *buffer, char** args,
size_t args_size, size_t *nargs)
{
char *buf_args[args_size]; /* You need C99 */
char **cp;
char *wbuf;
size_t i, j;
wbuf=buffer;
buf_args[0]=buffer;
args[0] =buffer;
for(cp=buf_args; (*cp=strsep(&wbuf, " \n\t")) != NULL ;){
if ((*cp != '\0') && (++cp >= &buf_args[args_size]))
break;
}
for (j=i=0; buf_args[i]!=NULL; i++){
if(strlen(buf_args[i])>0)
args[j++]=buf_args[i];
}
*nargs=j;
args[j]=NULL;
}
int main(int argc, char *argv[], char *envp[]){
char buffer[BUFFER_SIZE];
char *args[ARR_SIZE];
int *ret_status;
size_t nargs;
pid_t pid;
while(1){
printf("$ ");
fgets(buffer, BUFFER_SIZE, stdin);
parse_args(buffer, args, ARR_SIZE, &nargs);
if (nargs==0) continue;
if (!strcmp(args[0], "exit" )) exit(0);
pid = fork();
if (pid){
printf("Waiting for child (%d)\n", pid);
pid = wait(ret_status);
printf("Child (%d) finished\n", pid);
} else {
if( execvp(args[0], args)) {
puts(strerror(errno));
exit(127);
}
}
}
return 0;
}