C++ 向量vector和模板的应用

     C++里面的vector提供了对array/list的操作功能, 如下代码演示了如何建立vector并进行增加元素/查找元素/删除元素/枚举元素, 还演示了如何应用模板(template)来实现通用数据的vector打印.

#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>

#include "stdafx.h"
#include <stdio.h>
#include <iostream>
#include <vector>
using namespace std;

template<typename _T>
void printVector(_T pvvtSrc) {
	cout << endl;
	for (_T::iterator lvnItem = pvvtSrc.begin(); lvnItem != pvvtSrc.end(); lvnItem++) {
		cout << *lvnItem << " ";
	}
	cout << endl << "vector size: " << pvvtSrc.size() << endl;
}

template<class _C>
void printVectorC(_C pvvtSrc) {
	cout << endl;
	for (_C::iterator lvnItem = pvvtSrc.begin(); lvnItem != pvvtSrc.end(); lvnItem++) {
		cout << (*lvnItem).data() << " ";
	}
	cout << endl << "vector size: " << pvvtSrc.size() << endl;
}

void testVectorChars() {
	vector<string> lvvtChars;
	lvvtChars.push_back("one");
	lvvtChars.push_back("two");
	lvvtChars.push_back("three");
	printVectorC(lvvtChars);
	//查找元素
	vector<string>::iterator lvnItem = find(lvvtChars.begin(), lvvtChars.end(), "three");
	if (lvnItem != lvvtChars.end()) { //找到,则删除
		lvvtChars.erase(lvnItem);
	}
	printVectorC(lvvtChars);

}
void testVector() {
	vector<int> lvvtInts;
	//增加元素
	lvvtInts.push_back(5);
	lvvtInts.push_back(4);
	lvvtInts.push_back(3);
	lvvtInts.push_back(1);
	printVector(lvvtInts);
	//查找元素
	vector<int>::iterator lvnItem = find(lvvtInts.begin(), lvvtInts.end(), 3);
	if (lvnItem != lvvtInts.end()) { //找到,则删除
		lvvtInts.erase(lvnItem);
	}
	printVector(lvvtInts);

	lvvtInts.insert(find(lvvtInts.begin(), lvvtInts.end(), 1), 2); //在1的前面插入2
	printVector(lvvtInts);
	
	lvvtInts.insert(find(lvvtInts.begin(), lvvtInts.end(), 2), 3); //在2的前面插入3
	lvvtInts.insert(find(lvvtInts.begin(), lvvtInts.end(), 2), 3); //在2的前面插入3
	printVector(lvvtInts);

	//删除所有3
	for (vector<int>::iterator lvnItem = lvvtInts.begin(); lvnItem != lvvtInts.end(); lvnItem++) {
		if (*lvnItem != 3)continue;
		lvnItem=lvvtInts.erase(lvnItem);
		lvnItem--;
	}	
	printVector(lvvtInts);
	
}
int main(int argc, char* argv[])
{
	_CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
	testVector();
	testVectorChars();
	getchar();
	return 0;
}

上面代码, 由于string是一个类,所以template<typename _T>不通用, 只能重新用template<class _C>定义一个类相关的模板.

运行结果:

5 4 3 1
vector size: 4

5 4 1
vector size: 3

5 4 2 1
vector size: 4

5 4 3 3 2 1
vector size: 6

5 4 2 1
vector size: 4

one two three
vector size: 3

one two
vector size: 2

----------------

vector 与数组的互相转换:

//测试小数数组与vector的互相转换
void testFloatArrsVector() {
	
	float lvflItems[] = { 1.1f,2.2f,3.3f,4.4f,5.5f };
	// float arrays to vector
	vector<float> lvvfItems (lvflItems, lvflItems + sizeof(lvflItems) / sizeof(float));
	printVector(lvvfItems);
	//亦可以通过下标直接访问元素
	for (size_t i = 0; i < lvvfItems.size(); i++) {
		cout << lvvfItems[i] << endl;
	}
	//vector to float arrays
	if (!lvvfItems.empty()){
		float* lvflNew =  new float[lvvfItems.size()];
		memcpy(lvflNew, &lvvfItems[0], lvvfItems.size() * sizeof(float));
		//print float array
		for (size_t i = 0; i < lvvfItems.size(); i++) {
			cout << lvflNew[i] << "  ";
		}
		delete[]lvflNew;
		cout << endl;

		// 或者直接指向vector的内存块,将其转换为数组来用.
		float *lvflpt = &lvvfItems[0];
		for (size_t i = 0; i < lvvfItems.size(); i++) {
			cout << lvflpt[i] << "  ";
		}
	}
}

从上述代码演示了从数组转vector和从vector转数组,  在vector转数组用了两种方法, 一种是先将数据做了一份拷贝再使用, 另一种方法是可以直接用 &lvvfItems[0]和lvvfItems.size()作为数组数据来用了.