C中的system()时出现分段错误

我想使用 linux的“base64”脚本对数据进行编码并在C中获取.
当我尝试编译

char a[200];
strcpy(a, "Hello");
printf("%s", a);

我得到了输出

Hello

现在,每当我尝试代码

char a[200];
strcpy(a, system("echo Hello | base64"));
printf("%s", a);

我得到了输出

aGVsbG8K
Segmentation fault

即使我删除了“printf”语句,我也是如此

aGVsbG8K
Segmentation fault

我想保存输出的值

system("echo Hello | base64")

在’a’而不显示它.请帮忙

这里

strcpy(a, system("echo Hello | base64"));

system()不会将其结果存储到数组a中,因为system()作业是执行参数&中提供的命令.将它打印在控制台上,即stdout缓冲区.从system的手册页

system() executes a command specified in command by calling
/bin/sh -c
command, and returns after the command has been completed.

有一种方法可以解决这个问题,即不是在stdout上打印system()输出,而是可以将其输出重定向到文件&然后从文件&中读取打印.例如

int main(void) {
        close(1); /* stdout file descriptor is avilable now */
        /* create the file if doesn't exist, if exist truncate the content to 0 length */
        int fd = open("data.txt",O_CREAT|O_TRUNC|O_RDWR,0664); /* fd gets assigned with lowest 
                                                  available fd i.e 1 i.e nowonwards stdout output 
                                                  gets rediredcted to file */
        if(fd == -1) {
                /* @TODO error handling */
                return 0;
        }
        system("echo Hello | base64"); /* system output gets stored in file */
        int max_char = lseek(fd,0,2);/* make fd to point to end, get the max no of char */
        char *a = malloc(max_char + 1); /* to avoid buffer overflow or 
                underflow, allocate memory only equal to the max no of char in file */
        if(a == NULL) {
                /* @TODO error handling if malloc fails */
                return 0;
        }
        lseek(fd,0,0);/* from beginning of file */
        int ret = read(fd,a,max_char);/* now read out put of system() from
                                          file as array and print it */
        if(ret == -1) {
                /* @TODO error handling */
                return 0;
        }
        a[ret] = '\0';/* \0 terminated array */
        dup2(0,fd);/*fd 0 duplicated to file descriptor where fd points i.e */
        printf("output : %s \n", a);
        /* to avoid memory leak, free the dynamic memory */
        free(a);
        return 0;
}

我的上述建议是一个临时修复&我不会推荐这个,而是按照@chris Turner(http://man7.org/linux/man-pages/man3/popen.3.html)的建议使用[popen]

The popen() function opens a process by creating a pipe, forking,
and
invoking the shell. Since a pipe is by definition unidirectional, the
type argument may specify only reading or writing, not both; the
resulting stream is correspondingly read-only or write-only.

例如

int main(void) {
        char buf[1024];
        FILE *fp = popen("echo Hello | base64","r");
        printf("%s\n",fgets(buf,sizeof(buf),fp));
        return 0;
}