c - 关于我的发送的问题 - 动态分配

Question

我正在研究有关动态分配的学生项目，我认为我的发送有问题，有人可以帮忙吗？

void buildBoard(int*** mat, int size);
void initMat(int*** mat, int size);

int main()
{
    int size;
    int** mat;
    printf("Please enter a size of the matrix:\n");
    scanf("%d", &size);
    buildBoard(&mat, size);
    initMat(&mat, size);
    for (int i = 0; i < size; ++i)
    {
        for (int j = 0; j < size; ++j)
        {
            printf("%d ", mat[i][j]);
        }
        printf("\n");
    }
    return 0;
}

void buildBoard(int*** mat, int size)
{
    *mat = (int**)malloc(size * sizeof(int*));
    if (*mat == NULL)
    {
        printf("Bye\n");
        exit(1);
    }
    for (int i = 0; i < size; ++i)
    {
        mat[i] = (int*)malloc(size * sizeof(int));
        if (mat[i] == NULL)
        {
            printf("Bye\n");
            free(mat[i]);
        }
    }
}

void initMat(int*** mat, int size)
{
    int num;
    printf("Please enter a numbers:\n");
    for (int i = 0; i < size; ++i)
    {
        for (int j = 0; j < size; ++j)
        {
            scanf("%d", &mat[i][j]);
        }
    }
}

在主函数中，我想检查我的分配，但打印时它总是崩溃。

Answer 1

您错过了多次取消引用mat，我的意思是某些mat必须是(*mat):

void buildBoard(int*** mat, int size)
{
    *mat = (int**)malloc(size * sizeof(int*));
    if (*mat == NULL)
    {
        printf("Bye\n");
        exit(1);
    }
    for (int i = 0; i < size; ++i)
    {
        (*mat)[i] = (int*)malloc(size * sizeof(int));
        if ((*mat)[i] == NULL)
        {
            printf("Bye\n");
            exit(1);
        }
    }
}

void initMat(int*** mat, int size)
{
    printf("Please enter a numbers:\n");
    for (int i = 0; i < size; ++i)
    {
        for (int j = 0; j < size; ++j)
        {
            scanf("%d", &(*mat)[i][j]);
        }
    }
}

我还删除了无用的变量num

编译和执行:

pi@raspberrypi:/tmp $ gcc -g -pedantic -Wall c.c
pi@raspberrypi:/tmp $ ./a.out
Please enter a size of the matrix:
2
Please enter a numbers:
1
2
3
4
1 2 
3 4 

在 valgrind 下:

pi@raspberrypi:/tmp $ valgrind ./a.out
==4232== Memcheck, a memory error detector
==4232== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==4232== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==4232== Command: ./a.out
==4232== 
Please enter a size of the matrix:
2
Please enter a numbers:
1
2
3
4
1 2 
3 4 
==4232== 
==4232== HEAP SUMMARY:
==4232==     in use at exit: 24 bytes in 3 blocks
==4232==   total heap usage: 5 allocs, 2 frees, 2,072 bytes allocated
==4232== 
==4232== LEAK SUMMARY:
==4232==    definitely lost: 8 bytes in 1 blocks
==4232==    indirectly lost: 16 bytes in 2 blocks
==4232==      possibly lost: 0 bytes in 0 blocks
==4232==    still reachable: 0 bytes in 0 blocks
==4232==         suppressed: 0 bytes in 0 blocks
==4232== Rerun with --leak-check=full to see details of leaked memory
==4232== 
==4232== For counts of detected and suppressed errors, rerun with: -v
==4232== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)
pi@

当然valgrind表示内存泄漏，因为您没有释放分配的内存

<小时/>

注意，将变量的地址赋予initMat是没有用的，可以是:

void initMat(int** mat, int size)
{
    printf("Please enter a numbers:\n");
    for (int i = 0; i < size; ++i)
    {
        for (int j = 0; j < size; ++j)
        {
            scanf("%d", &mat[i][j]);
        }
    }
}

当然也改变了它的声明和main中的调用

<小时/>

之前我还删除了您在以下位置的免费:

    if (mat[i] == NULL)
    {
        printf("Bye\n");
        free(mat[i]);
    }

因为事实上你释放了 NULL