[C++知识库]c/c++动态二维数组创建与修改

?C中动态内存的分配通过malloc创建

int* p=(int*)malloc(sizeof(int));

?创建了一个大小为int的内存段

创建多字节内存段

int*p=(int*)malloc(sizeof(int)*3);

?创建4行3列动态二维数组

使用二级指针指向一维数组（里面存储是一级指针），每个一级指针指向一段内存段。

打印验证

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

int main()
{
	int** p = (int**)malloc(sizeof(int*)*4);
	for (size_t i = 0; i < 4; i++)
	{
		p[i] = (int*)malloc(sizeof(int)*3);
	}
	//赋值 并打印
	for (size_t i = 0; i < 4; i++)
	{
		for (size_t j = 0; j < 3; j++)
		{
			p[i][j] = i * j;
			printf("%d\t", p[i][j]);
		}
		printf("\n");
	}
	printf("\n");


	return 0;
}

C++动态内存申请

#include<iostream>
using namespace std;

int main()
{
	int** pp = new int* [4];

	for (size_t i = 0; i < row; i++)
	{
		pp[i] = new int[3];
	}
	//初始化数据
	for (int i = 0; i < 4; i++)
	{
		for (int j = 0; j < 3; j++)
		{
			pp[i][j] = i * j;
			printf("%d\t", pp[i][j]);
		}
		printf("\n");
	}


	return 0;
}

?以下代码通过传参方式修改数据

C形参是三级指针方式，C++形参采用引用方式

#include<iostream>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
int** createArray2D(int row, int cols)
{
	//int *pArray=(int*)malloc(sizeof(int)*3)
	int** pArray = (int**)malloc(sizeof(int*) * row);
	if (pArray == NULL)
		return NULL;
	for (int i = 0; i < row; i++)
	{
		//一级指针
		pArray[i] = (int*)malloc(sizeof(int) * cols);

	}
	return pArray;
}
//传参修改二维数组动态分配
void mallocArray2D(int*** pArray, int row, int col)
{
	for (size_t i = 0; i < row; i++)
	{
		for (size_t j = 0; j < col; j++)
		{
			(*pArray)[i][j] = i + 2 * j;
		}
		printf("\n");
	}
}

//C++创建二维动态数组
int** createArray2DByNew(int row, int col)
{
	int** pp = new int* [row];
	if (pp == nullptr)
		return nullptr;
	for (size_t i = 0; i < row; i++)
	{
		pp[i] = new int[col];
	}
	return pp;
	
}
//引用方式修改
void modifyArray2D(int**& pArray,int row,int col)
{
	for (size_t i = 0; i < row; i++)
	{
		for (size_t j = 0; j < col; j++)
		{
			pArray[i][j] = i * j + 2;
		}
	}
}


int main()
{
	//c申请
#if 0
	int** p = createArray2D(4, 3);
	for (int i = 0; i < 4; i++)
	{
		for (int j = 0; j < 3; j++)
		{
			p[i][j] = i * j;
			printf("%d\t", p[i][j]);
		}
		printf("\n");
	}
	mallocArray2D(&p, 4, 3);
	for (int i = 0; i < 4; i++)
	{
		for (int j = 0; j < 3; j++)
		{

			printf("%d\t", p[i][j]);
		}
		printf("\n");
	}
#endif
#if 1
	//C++申请
	int* p = new int[3];
	//int** pp = new int* [5];

	int **pp=createArray2DByNew(4,3);
	//初始化数据
	for (int i = 0; i < 4; i++)
	{
		for (int j = 0; j < 3; j++)
		{
			pp[i][j] = i * j;
			printf("%d\t", pp[i][j]);
		}
		printf("\n");
	}
	//修改数据
	modifyArray2D(pp,4,3);
	//输出
	cout << endl;
	
	for (size_t i = 0; i < 4; i++)
	{
		for (size_t j = 0; j < 3; j++)
		{
			cout << pp[i][j] <<"\t";
		}
		cout << endl;
	}
#endif
	return 0;
}