我正在学习在linux中使用普通管道进行父子进程之间通信的方法。基本任务只是从父进程向子进程发送消息,然后子进行一些转换并将结果传递回父进程。我显示的结果是一些随机字符,如 。我已经考虑了很长一段时间,仍然无法弄清楚这个bug。谢谢你的帮助。
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#define READ_END 0
#define WRITE_END 1
void convert(char* str);
int main(int argc, char *argv[]){
int pid; /* Process ID */
int status;
char *input;
char *read_msg_c;
char *read_msg_p;
int pfd1[2], pfd2[2];
if (argc !=2){/* argc should be 2 for correct execution */
/* We print argv[0] assuming it is the program name */
printf("Please provide the string for conversion \n");
exit(-1);
}
input = argv[1];
if(pipe(pfd1) < 0 || pipe(pfd2) < 0){
printf("Failed to create a pipe between parent and child \n");
exit(-1);
}
if((pid = fork()) < 0){ /* Fork the process */
printf("Fork error \n");
exit(-1);
}
else if(pid > 0){ /* Parent code */
close(pfd1[READ_END]);
close(pfd2[WRITE_END]);
printf("Process ID of the parent is %d. \n", getpid()); /* Print parent's process ID */
write(pfd1[WRITE_END],input,strlen(input)+1);
close(pfd1[WRITE_END]);
read(pfd2[READ_END],read_msg_p,strlen(input)+1);
printf("%s\n",read_msg_p);
close(pfd2[READ_END]);
}
else if(pid == 0){ /* Child code */
close(pfd1[WRITE_END]);
close(pfd2[READ_END]);
printf("Process ID of the child is %d. \n", getpid()); /* Print child's process ID */
read(pfd1[READ_END],read_msg_c, strlen(input)+1);
printf("Child: Reversed the case of the received string. \n");
write(pfd2[WRITE_END],read_msg_c,strlen(input)+1);
close(pfd1[READ_END]);
close(pfd2[WRITE_END]);
exit(0); /* Child exits */
}
}
void convert(char *str){
int i = 0;
while (str[i]){
if (isupper(str[i])){
str[i] = tolower(str[i]);
}
else if (islower(str[i])){
str[i] = toupper(str[i]);
}
i++;
}
}
答案 0 :(得分:2)
您的主要错误是您的变量read_msg_p
和read_msg_c
是未初始化的指针。
将它们变成数组:
char read_msg_p[1024];
char read_msg_c[1024];
您似乎缺少<stdio.h>
(但您不再需要<sys/types.h>
)。你应该错误地检查你的读写;一旦为其分配了空间,您的读取可能会使用不同的最大大小。等
我通过查看编译器警告来发现问题:
$ gcc -O3 -g -std=c99 -Wall -Wextra pipes-14420398.c -o pipes-14420398
pipes-14420398.c: In function ‘main’:
pipes-14420398.c:40:22: warning: ‘read_msg_p’ may be used uninitialized in this function [-Wuninitialized]
pipes-14420398.c:52:22: warning: ‘read_msg_c’ may be used uninitialized in this function [-Wuninitialized]
$
忽略行号;当这些是唯一的警告时,我会适度地严重破解你的代码。但有问题的行是read()
电话。
示例输出形成被黑客入侵的代码,正常工作。
$ ./pipes-14420398 string-to-convert
Process ID of the parent is 37327.
Process ID of the child is 37328.
Child read 18 bytes: <<string-to-convert>>
Parent read 18 bytes: <<string-to-convert>>
$
请注意,下面的代码读取18个字节(包括null),但不打印null(因为nbytes-1
的{{1}}参数。
printf()
如WhozCraig所述,还有许多其他变化可以做出。然而,这使得事情合理地干净利落。你非常接近OK。
请注意调试技巧: