C结构破解工作 [英] C struct hack at work

问题描述

这是在使用C结构黑客可以如何使用分配的额外的内存？

问题：

我有以下的C结构黑客实施。我的问题是如何使用，我已经与黑客分配的额外的内存。是否有人可以给我一个例子使用了额外的内存？

 ＃包括LT＆;＆stdio.h中GT;
＃包括LT＆;＆stdlib.h中GT;诠释的main（）
{    结构MYSTRUCT {        INT LEN;
        炭chararray [1];    };    结构MYSTRUCT * PTR =的malloc（sizeof的（结构MYSTRUCT）+ 10  -  1）;
    ptr-＆GT;的len = 10;
    ptr-＆GT; chararray [0] ='A';
    ptr-＆GT; chararray [1] ='B';
    ptr-＆GT; chararray [2] ='c'的;
    ptr-＆GT; chararray [3] ='D';
    ptr-＆GT; chararray [4] ='E';
    ptr-＆GT; chararray [5] = f的;
    ptr-＆GT; chararray [6] =G;
    ptr-＆GT; chararray [7] =H;
    ptr-＆GT; chararray [8] ='我';
    ptr-＆GT; chararray [9] ='J';
}
 

解决方案

是的，这是（并且是）在 C 的标准方式创建和处理variably-大小结构。

这例子是一个有点冗长。大多数程序员会更巧妙地处理它：

 结构MYSTRUCT {
        INT LEN;
        炭chararray [1]; //有些编译器允许[0]这里
    };
    字符*味精=ABCDEFGHI;
    INT N = strlen的（MSG）;    结构MYSTRUCT * PTR =的malloc（sizeof的（结构MYSTRUCT）+ N + 1）;    ptr-＆GT; LEN = N;
    的strcpy（ptr-＆GT; chararray，味精）;
}
 

Is this how one can use the the "extra" memory allocated while using the C struct hack?

Questions:

I have a C struct hack implementation below. My question is how can I use the "extra" memory that I have allocated with the hack. Can someone please give me an example on using that extra memory ?

#include<stdio.h>
#include<stdlib.h>

int main()
{

    struct mystruct {

        int len;
        char chararray[1];

    };

    struct mystruct *ptr = malloc(sizeof(struct mystruct) + 10 - 1);
    ptr->len=10;


    ptr->chararray[0] = 'a';
    ptr->chararray[1] = 'b';
    ptr->chararray[2] = 'c';
    ptr->chararray[3] = 'd';
    ptr->chararray[4] = 'e';
    ptr->chararray[5] = 'f';
    ptr->chararray[6] = 'g';
    ptr->chararray[7] = 'h';
    ptr->chararray[8] = 'i';
    ptr->chararray[9] = 'j';


}

解决方案

Yes, that is (and was) the standard way in C to create and process a variably-sized struct.

That example is a bit verbose. Most programmers would handle it more deftly:

struct mystruct {
        int len;
        char chararray[1];  // some compilers would allow [0] here
    };
    char *msg = "abcdefghi";
    int n = strlen (msg);

    struct mystruct *ptr = malloc(sizeof(struct mystruct) + n + 1);

    ptr->len = n;
    strcpy (ptr->chararray, msg);
}

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