在C语言中进行字符串操作时，遇到分段故障。

Question

我正在努力从C语言的主字符串中删除一个子串的混淆，这个子串的格式是 xx:xx:xx:xx:xx:xx 哪儿 x 可以是一个数字或字母。子串的开头总是有一个空格，但子串的结尾并不总是有一个空格。

e.x. 输入可以是 "Found new device with wlan 33:33:33:33:33:33. Total 4 devices connected" 输出应该是 "Found new device with wlan *. Total 4 devices connected"

我需要做一个辅助函数来实现，这就是我想出的办法。

//find the first occurency of ":" record as first_position_ptr and the last occurency of ":" record as last_position_ptr. 
// Add 2 to first_position_ptr to beginning of the substring and set it to "*"
// Subtract 2 from the last_position_ptr to get the pointer of the last charactor in substrung. 
// Iterate from 1 + first_position_ptr to last_position_ptr - 2 and set inStr to 0 to deleted the rest of substring. 

const char *proc(char *inStr) {
    const char tar[] = ":";
    char *first_position_ptr = strchr(inStr, tar[0]);
    char *last_position_ptr = strrchr(inStr, tar[0]);

    int first_position = (first_position_ptr == NULL ? -1 : first_position_ptr - inStr);
    int last_position = (last_position_ptr == NULL ? -1 : last_position_ptr - inStr);

    if (first_position != -1 && last_position != -1) {
        inStr[first_position + 2] = "*";
    }

    for (int i = (first_position + 1); i < (last_position + 2); i++) {
        inStr[i] = 0;
    }
    return inStr;
}

int main() {
    const char str[] = "Found new device with wlan 33:33:33:33:33:33. Total 4 devices connected";
    proc(*str);
    printf("%s\n", str);
    return 0;
}

但当我编译代码时，我遇到了这些警告。

Jeff-MacBook-Pro-2:Desktop jBerman$ gcc test.c -o test
test.c:35:29: warning: incompatible pointer to integer conversion assigning to 'char' from
      'char [2]' [-Wint-conversion]
                inStr[first_position + 2] = "*";
                                          ^ ~~~
test.c:43:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^
test.c:49:7: warning: incompatible integer to pointer conversion passing 'const char' to
      parameter of type 'char *' [-Wint-conversion]
        proc(*str);
             ^~~~
test.c:26:24: note: passing argument to parameter 'inStr' here
const char* proc(char *inStr){
                       ^
3 warnings generated.

当我运行它时，编译说：

Segmentation fault: 11

所以我试着在main中改正这行。

proc(*str) -> proc(&str);

编译器返回：

Bus error: 10

谁能告诉我可能出了什么问题？或者如果你有更有效的方法，请告诉我。

Answer 1

你应该通过 str 到 proc，不 *str 并定义 str 作为一个可修改的 char 数组。proc 函数也应该简化：将中间的字符设置为零，并不会擦掉中间的部分，而是让字符串在后面的 *. 要保留字符串的结尾，你必须用 memmove().

这里是一个修改版。

#include <stdio.h>
#include <string.h>

// replace the mac address from the input string with a *
char *proc(char *inStr) {
    char *p1 = strchr(inStr, ':');
    char *p2 = strrchr(inStr, ':');

    if (p1) {  // no need to test p2, there is at least one ':' in the string
        /* backtrack 2 characters, but not before the start of inStr */
        if (p1 > inStr) p1--;
        if (p1 > inStr) p1--;
        /* skip 3 characters, but not past the end of the string */
        p2++;
        if (*p2) p2++;
        if (*p2) p2++;
        /* replace the MAC address with a '*' */
        *p1++ = '*';
        /* move the rest of the string, including the null terminator */
        memmove(p1, p2, strlen(p2) + 1);
    }
    return inStr;
}

int main() {
    char str[] = "Found new device with wlan 33:33:33:33:33:33. Total 4 devices connected";
    printf("%s\n", proc(str));
    return 0;
}