c中结构指针内的双数组

Question

为什么这个双映射数组几乎可以工作，但没有？

我的代码如下：

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

typedef struct {
    double mapping [3][3];
} CoordinateMapperStr;
typedef CoordinateMapperStr * CoordinateMapper;

CoordinateMapper CoordinateMapper_Constructor(void)
{
    CoordinateMapper this = (CoordinateMapper) calloc (1, sizeof(CoordinateMapper));
    //return this; // <- I was missing this return, but still the rest worked the same
}

void CoordinateMapper_Initialize(CoordinateMapper this, double numb)
{
    for (int i=0; i < 3; i=i+1) {
        for (int j=0; j < 3; j=j+1) {
            this->mapping[i][j] = numb;
            printf("mapping(%d, %d) = %f\n", i, j, this->mapping[i][j]);
        }
    }
}

void CoordinateMapper_Print(CoordinateMapper this)
{
    for (int i=0; i < 3; i=i+1) {
        for (int j=0; j < 3; j=j+1) {
            printf("mapping(%d, %d) = %f\n", i, j, this->mapping[i][j]);
        }
    }
}

int main()
{
    CoordinateMapper mapper_1 = CoordinateMapper_Constructor();
    CoordinateMapper_Initialize(mapper_1, 1);
    printf("Init 1 done\n");

    CoordinateMapper_Print(mapper_1);
    printf("Print 1 done\n");

    CoordinateMapper mapper_2 = CoordinateMapper_Constructor();
    CoordinateMapper_Initialize(mapper_2, 2);
    printf("Init 2 done\n");

    CoordinateMapper_Print(mapper_1);
    printf("Second print 1 done\n");

    CoordinateMapper_Print(mapper_2);
    printf("Print 2 done\n");
}

// Here is the corresponding output
user:~/path$ gcc src/test_3.c -o test_3
user:~/path$ ./test_3
mapping(0, 0) = 1.000000
mapping(0, 1) = 1.000000
mapping(0, 2) = 1.000000
mapping(1, 0) = 1.000000
mapping(1, 1) = 1.000000
mapping(1, 2) = 1.000000
mapping(2, 0) = 1.000000
mapping(2, 1) = 1.000000
mapping(2, 2) = 1.000000
Init 1 done
mapping(0, 0) = 1.000000
mapping(0, 1) = 1.000000
mapping(0, 2) = 1.000000
mapping(1, 0) = 1.000000
mapping(1, 1) = 0.000000 // This is not correct
mapping(1, 2) = 0.000000 // This is not correct
mapping(2, 0) = 0.000000 // This is not correct
mapping(2, 1) = 1.000000
mapping(2, 2) = 1.000000
Print 1 done
mapping(0, 0) = 2.000000
mapping(0, 1) = 2.000000
mapping(0, 2) = 2.000000
mapping(1, 0) = 2.000000
mapping(1, 1) = 2.000000
mapping(1, 2) = 2.000000
mapping(2, 0) = 2.000000
mapping(2, 1) = 2.000000
mapping(2, 2) = 2.000000
Init 2 done
mapping(0, 0) = 1.000000
mapping(0, 1) = 1.000000
mapping(0, 2) = 1.000000
mapping(1, 0) = 1.000000
mapping(1, 1) = 0.000000 // This is not correct
mapping(1, 2) = 0.000000 // This is not correct
mapping(2, 0) = 0.000000 // This is not correct
mapping(2, 1) = 1.000000
mapping(2, 2) = 1.000000
Second print 1 done
mapping(0, 0) = 2.000000
mapping(0, 1) = 2.000000
mapping(0, 2) = 2.000000
mapping(1, 0) = 2.000000
mapping(1, 1) = 2.000000
mapping(1, 2) = 2.000000
mapping(2, 0) = 2.000000
mapping(2, 1) = 2.000000
mapping(2, 2) = 2.000000
Print 2 done

在结构指针中设置双精度数组的正确方法是什么？
为什么每个结构指针似乎都创建了自己的新数组，但它们仍然有点不稳定？
我可以使用哪些 gcc 编译器标志来帮助我查看此类错误以及构造函数中缺少的 return this;？

Answer 1

问题是无论您是否return this，在任何一种情况下您都会遇到未定义的行为。

当你不 return this 你的非空函数没有 return 一个值——因此你的代码使用了一些垃圾值（这可能恰好是 return 值来自 calloc).

如果你return this——你return分配了sizeof(CoordinateMapper)，这只是单个指针的大小。这小于您的结构 sizeof(CoordinateMapperStr)，而您的其他代码 reads/writes 超出分配的内存。这又是未定义的行为。

Answer 2

@YakovGalka 发现了我的错误。这里要补充一点，valgrind确实是一个可以检测这类编程错误的工具。通过将 -Wall 和 -g 作为编译器标志添加到 gcc 和运行带有 valgrind ./compiled_app 的应用程序，然后很容易检测到这些类型的错误。

c中结构指针内的双数组

Double array within a struct pointer in c

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