铸造的char [] []到char **导致段错误？ [英] casting char[][] to char** causes segfault?

问题描述

好吧我的C是有点生疏，但我想我会做用C我的下一个（小）的项目，所以我可以擦亮备份就可以了不到20行的我已经有一个赛格故障。

Ok my C is a bit rusty but I figured I'd make my next(small) project in C so I could polish back up on it and less than 20 lines in I already have a seg fault.

这是我的完整code：

This is my complete code:

#define ROWS 4
#define COLS 4

char main_map[ROWS][COLS+1]={
  "a.bb",
  "a.c.",
  "adc.",
  ".dc."};

 void print_map(char** map){
  int i;
  for(i=0;i<ROWS;i++){
    puts(map[i]); //segfault here
  }
 }



int main(){
  print_map(main_map); //if I comment out this line it will work.
  puts(main_map[3]);
  return 0;
}

我来这是如何造成段错误完全糊涂了。从 [] [] 铸造时发生了什么** ！？这是唯一的警告，我得到。

I am completely confused as to how this is causing a segfault. What is happening when casting from [][] to **!? That is the only warning I get.

rushhour.c:23:3: warning: passing argument 1 of ‘print_map’ from incompatible pointer type
rushhour.c:13:7: note: expected ‘char **’ but argument is of type ‘char (*)[5]’

是 [] [] 和 ** 真的不兼容的指针类型？他们看起来他们只是语法我。

Are [][] and ** really not compatible pointer types? They seem like they are just syntax to me.

推荐答案

A 的char [行数] [COLS + 1] 不能转换成字符** 。 print_map 的输入参数应该是

A char[ROWS][COLS+1] cannot be cast into a char**. The input argument of print_map should be

void print_map(char map[][COLS+1])

或

void print_map(char (*map)[COLS+1])

---

区别在于一个的char ** 表示为指向的东西，可以解除引用如下：

---

The difference being that a char** means to point to something that can be dereferenced like this:

   (char**)map
       |
       v
  +--------+--------+------+--------+-- ...
  | 0x1200 | 0x1238 | NULL | 0x1200 |
  +----|---+----|---+--|---+----|---+-- ...
       v        |      =        |
    +-------+   |               |
    | "foo" | <-----------------'
    +-------+   |
                v
             +---------------+
             | "hello world" |
             +---------------+

而在字符（*）[N] 是一个点，这样的连续内存区域

While a char(*)[n] is a points to a continuous memory region like this

   (char(*)[5])map
       |
       v
  +-----------+---------+---------+-------------+-- ...
  | "foo\0\0" | "hello" | " worl" | "d\0\0\0\0" |
  +-----------+---------+---------+-------------+-- ...

如果你把一个（CHAR（*）[5]）为（字符**）你让垃圾：

If you treat a (char(*)[5]) as a (char**) you get garbage:

   (char**)map
       |
       v
  +-----------+---------+---------+-------------+-- ...
  | "foo\0\0" | "hello" | " worl" | "d\0\0\0\0" |
  +-----------+---------+---------+-------------+-- ...
      force cast (char[5]) into (char*):
  +----------+------------+------------+------------+-- ...
  | 0x6f6f66 | 0x6c686500 | 0x77206f6c | 0x646c726f |
  +----|-----+---------|--+------|-----+------|-----+-- ...
       v               |         |            |
    +---------------+  |         |            v
    | "hsd®yœâñ~22" |  |         |       launch a missile
    +---------------+  |         |
                       v         v
               none of your process memory
                        SEGFAULT

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