C语言进阶课程学习记录-第38课 - 动态内存分配

内存动态分配

实验-malloc(0)

#include <stdio.h>
#include <malloc.h>

int main()
{
    int i = 0;
    int* pI = (int*)malloc(0 * sizeof(int));
    printf("pI=%p\n", pI);
    free(pI);
    return 0;
}

    /*
    output:
pI=00032D08

    */

实验

#define MALLOC(n) mallocEx(n, __FILE__, __LINE__)
#define FREE(p) freeEx(p)

void* mallocEx(size_t n, const char* file, const line);//扩展malloc
void freeEx(void* p);
void PRINT_LEAK_INFO();

#include "mleak.h"

#define SIZE 256

/* 动态内存申请参数结构体 */
typedef struct
{
    void* pointer;//记录指针
    int size;//记录长度
    const char* file;//记录所在文件
    int line;//记录所在行
} MItem;

static MItem g_record[SIZE]; /* 记录动态内存申请的操作 */

void* mallocEx(size_t n, const char* file, const line)
{
    void* ret = malloc(n); /* 动态内存申请 */
    
    if( ret != NULL )
    {
        int i = 0;
        
        /* 遍历全局数组，记录此次操作 */
        for(i=0; i<SIZE; i++)
        {
            /* 查找位置 */
            if( g_record[i].pointer == NULL )
            {
                g_record[i].pointer = ret;
                g_record[i].size = n;
                g_record[i].file = file;
                g_record[i].line = line;
                break;
            }
        }
    }
    
    return ret;
}

void freeEx(void* p)
{
    if( p != NULL )
    {
        int i = 0;
        
        /* 遍历全局数组，释放内存空间，并清除操作记录 */
        for(i=0; i<SIZE; i++)
        {
            if( g_record[i].pointer == p )
            {
                g_record[i].pointer = NULL;
                g_record[i].size = 0;
                g_record[i].file = NULL;
                g_record[i].line = 0;
                
                free(p);
                
                break;
            }
        }
    }
}

void PRINT_LEAK_INFO()
{
    int i = 0;
    
    printf("Potential Memory Leak Info:\n");
    
    /* 遍历全局数组，打印未释放的空间记录 */
    for(i=0; i<SIZE; i++)
    {
        if( g_record[i].pointer != NULL )
        {
            printf("Address: %p, size:%d, Location: %s:%d\n", g_record[i].pointer, g_record[i].size, g_record[i].file, g_record[i].line);
        }
    }
}

#include <stdio.h>
#include "mleak.h"

void f()
{
    MALLOC(100);
}

int main()
{
    int* p = (int*)MALLOC(3 * sizeof(int));

    f();

    p[0] = 1;
    p[1] = 2;
    p[2] = 3;

    FREE(p);

    PRINT_LEAK_INFO();

    return 0;
}

    /*
    output:
Potential Memory Leak Info:
Address: 00A52D40, size:100, Location: D:\Users\cy\Cxuexi\Test\test1.c:6

    */

实验-realloc和calloc

#include <stdio.h>
#include <malloc.h>

#define SIZE 5

int main()
{
    int i = 0;
    int* pI = (int*)malloc(SIZE * sizeof(int));
    short* pS = (short*)calloc(SIZE, sizeof(short));

    for(i=0; i<SIZE; i++)
    {
        printf("pI[%d] = %d, pS[%d] = %d\n", i, pI[i], i, pS[i]);
    }

    printf("Before: pI = %p\n", pI);

    pI = (int*)realloc(pI, 2 * SIZE * sizeof(int));

    printf("After: pI = %p\n", pI);

    for(i=0; i<10; i++)
    {
        printf("pI[%d] = %d\n", i, pI[i]);
    }

    free(pI);
    free(pS);

    return 0;
}

    /*
    output:
pI[0] = 14488680, pS[0] = 0
pI[1] = 14494984, pS[1] = 0
pI[2] = 0, pS[2] = 0
pI[3] = 0, pS[3] = 0
pI[4] = 0, pS[4] = 0
Before: pI = 00DD2D28
After: pI = 00DD1468
pI[0] = 14488680
pI[1] = 14494984
pI[2] = 0
pI[3] = 0
pI[4] = 0
pI[5] = 673215333
pI[6] = 691419256
pI[7] = 1667845468
pI[8] = 1869836146
pI[9] = 1394635878

    */

小结

动态内存分配是C语言中的强大功能
程序能够在需要的时候有机会使用更多的内存
malloc单纯的从系统中申请固定字节大小的内存
calloc能以类型大小为单位申请内存并初始化为0
realloc用于重置内存大小