Conversion between data types

Update your own notes from time to time:
1. QString and int

QString Str="123";
int i=Str.toInt();//同理long、double等
str=QString::number(i);
//注意：如果字符串非纯数字，最终转换int的结果为0

2，QString与string

 QString Qstr="123";
 string str=Qstr.toStdString();
 Qstr=QString::fromStdString(str);

3, string and int

 string str="123";
 int i=stoi(str);
 str=to_string(i);

3. const char* and string

 string str="123";
 const char* ch = str.c_str();
 // const char* ch = str.data(); 也可以
 str=ch;