C语言 动态内存分配的详解及实例

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

int main()
{
  int i=10;
  int* p= NULL;
  for(i=0;i<100;i++)
  {
    //注意，malloc(0)会返回一个有效的内存地址，大小为1
    //但我们不能依赖编译器的这种行为来使用这个字节的空间！
    p = (int*)malloc(i);
    printf("%d ",_msize(p));//返回malloc出来的内存空间大小
    free(p);
  }

  return 0;
}

#ifndef _MLEAK_H_
#define _MLEAK_H_

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

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

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

#endif

#include "mleak.h"

#define SIZE 256

//动态内存申请参数结构体
typedef struct
{
  void* pointer;//申请到的内存地址
  int size;   //内存块大小
  const char* file; //文件名
  int line;     //文件行号
}MItem;

static MItem g_record[SIZE]; //记录每个动态内存申请的操作

void* mallocEx(size_t n, const char* file, const line)
{
  int i = 0;
  void* ret = malloc(n);//动态内存申请
  
  if(ret != NULL)
  {
    //申请成功，则记录下来
    
    //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("Potenital Memory Leak Info:\n");

  //遍历全局数组，打印未释放的空间的申请记录
  for(i = 0; i< SIZE; i++)
  {
    //查找位置
    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()
{
  //没释放，会造成内存泄漏！
  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;
}

/*
输出结果：
E:\Study>gcc test.c mleak.c
E:\Study>a.exe
Potenital Memory Leak Info:
Address:00602ED8, size:100, Location:38-1.c:7
*/

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

#define SIZE  5

int main()
{
  int i = 0;
  int* pI = (int*)malloc(SIZE * sizeof(int)); //malloc内存没有初始化
  short* pS = (short*)calloc(SIZE, sizeof(short));//内存初始化为0

  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); //重置内存大小之前的pI指针

  pI = (int*)realloc(pI, 2 * SIZE * sizeof(int)); //内存未初始化的

  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;
}