C++数据类型转换

https://blog.csdn.net/thecentry/article/details/78477212

https://blog.csdn.net/LYH2277/article/details/82947649

1. c_str()：生成一个const char*指针，指向以空字符终止的数组。

2. data():与c_str()类似，但是返回的数组不以空字符终止。


编程中出现char* 与string/wstring/CString之间的转换;

//char* string 与int float double之间的转换.
以下为程序头文件:

#inlcude<iostream>
#include<string>
#include<ssrtream>
using namespace std;

char* char[] 与string 类型之间的转换;
int cp1()
{
  char *p = "abcd";
  char t[] = "abcde";
  string test;
  test = p;
  cout << test <<endl;
  cout << test.length() <<endl;
  return 0;
}


//string 到 char*的转换
int cp2()
{
  string test = "abc";
  char t[10];
  strcpy(t, test.c_str());
  cout << t << endl;
  cout << strlen(t) <<endl;
  
  char *te;
  int number = test.length();
  te = new char[number + 1];
  cout << number <<endl;
  
  strcpy(te, test.c_str());
  cout << te << endl;
  cout << strlen(te) << endl;
  
  delete[] te;
  return 0;
}

//string到const char*之间的转换:\
int CP3()
{
  const char* c;
  string test = "1234";
  c = test.c_str();
  cout << c <<endl;
  const char* t;
  t = test.data();
  cout << t << endl;
}

//int到string的转换

int CP4()
{
  int nt = 30;
  char c[30];
  
  //using C template to trans tfrom int to string
  itoa(nt, c, 10);//以参数3位为进制,以几进制转换为 char
  cout << c <<endl;
  cout << strlen(c) <<endl;
  
  //using string stream to trans from int to string 
  stringstream test;
  test << nt;
  string stest = test.str();
  cout << stest <<endl;
  cout << stest.length() << endl;
  
}

//sting到int的转换
int CP5()
{
  string test = "17";
  char* t;
  
  int nt = static_cast<int>(strtol(test.c_str(), &t, 10));//10 表示转换进制
  cout << nt <<endl;
  int nte;
  sscanf(test.c_str(), "%d", &nte);//%d 表示十进制
  cout << nte <<endl;
  
  //using stringstream to trans from string to int 
 stringstream stest;
 stest << test;
 int ntes;
 stest >> ntes;
 cout << ntes << endl;
 
 //using C template to trans from string tio int 
 int ntest = atoi(test.c_str());
 cout << ntest << endl;
 
 //using C++ template to trans from string to int
 int nnt;
 nnt = stoi(test.c_str());
 cout << nnt <<endl;
 return 0;
}

//string to double 的转换
int cp6()
{
    string test = "17.101";
    //using C template to trans from double to string 
    double t = atof(test.c_str());
    cout << t << endl;
    return 0;
}

数值类型到string的转换可以有以下几种:
(1)函数模板+stringstream
int 型转换为string型

void int2str(const int &int_temp,string &string_temp)
{
  stringstream stream(string_temp);
  stream << int_temp;
}

string型转int型

void str2int(int &int_temp,const string &string_temp)
{
  stringsrtream stream(string_temp);
  stream >> int_temp;
}

使用标准库函数std::to_string：
string to_string (int val);
string to_string (long val);
string to_string (long long val);
string to_string (unsigned val);
string to_string (unsigned long val);
string to_string (unsigned long long val);
string to_string (float val);
string to_string (double val);
string to_string (long double val);

使用C标准库函数：
atoi(str.c_str());
strtoul(str.c_str(), NULL, 10);
atof(str.c_str());

使用C++标准库函数：
stoi（）