[C++知识库]22 C++ string/int/long/float/double/char类型转换

#include<iostream>
#include <string>
#include <stdio.h>
#include <cstdlib>
#include <sstream>
using namespace std;

int conversion_type() {

	// string 转 int
	string num01_str = "123";
	int num01_int = atoi(num01_str.c_str());

	// string 转 long
	string num02_str = "9876543210";
	long num02_long = atol(num01_str.c_str());

	// string 转 float
	string num03_str = "9.8765";
	float num03_float = atof(num03_str.c_str());

	// string 转 double
	string num04_str = "1255639.8780913415";
	double num04_double;
	//方法1
	num04_double = atof(num04_str.c_str());//方法1
	// 
	//方法2
	//string::size_type size; 
	//num04_double = stod(num04_str, &size);
	//方法3
	//istringstream istrStream(num04_str);
	//istrStream >> num04_double;


	// string 转 char
	string num05_str = "hello";
	const char *num05_char= num05_str.c_str();
	
	printf("%d\n%d\n%f\n%f\n%s\n",num01_int, num02_long,num03_float,num04_double, num05_char);

	// int 转 string
	int a = 1;
	string b = to_string(a);

	// long 转 string
	long i = 1234567890;
	string j = to_string(i);
	// float 转 string
	float c = 3.1415;
	string d = to_string(c);

	// double 转 string
	double e = 3.1415926535;
	string f = to_string(e);
	// char 转 string
	const char *g = "world"; //一定要双引号
	string h = g;
	//cout << b <<endl<< d << endl << f << endl << h << endl;
	printf("%s\n%s\n%s\n%s\n%s", b.c_str(), j.c_str(), d.c_str(), f.c_str(), h.c_str());



	return 0;
}