IDEA激活码目录
文章适用于已经学了C++语言，对C++类型有一定了解的朋友。对类型转换进行总结，包括内置类型，string，以及由c语言引入的一些类型。
类型
| 内置数据类型 | 字节 | 范围 |
|---|---|---|
| char | 1 个字节 | -128 到 127 或者 0 到 255 |
| unsigned char | 1 个字节 | 0 到 255 |
| signed char | 1 个字节 | -128 到 127 |
| int | 4 个字节 | -2147483648 到 2147483647 |
| unsigned int | 4 个字节 | 0 到 4294967295 |
| signed int | 4 个字节 | -2147483648 到 2147483647 |
| short int | 2 个字节 | -32768 到 32767 |
| unsigned short int | 2 个字节 | 0 到 65,535 |
| signed short int | 2 个字节 | -32768 到 32767 |
| long int | 8 个字节 | -9,223,372,036,854,775,808 到 9,223,372,036,854,775,807 |
| signed long int | 8 个字节 | -9,223,372,036,854,775,808 到 9,223,372,036,854,775,807 |
| unsigned long int | 8 个字节 | 0 到 18,446,744,073,709,551,615 |
| float | 4 个字节 | 精度型占4个字节（32位）内存空间，+/- 3.4e +/- 38 (~7 个数字) |
| double | 8 个字节 | 双精度型占8 个字节（64位）内存空间，+/- 1.7e +/- 308 (~15 个数字) |
| long double | 16 个字节 | 长双精度型 16 个字节（128位）内存空间，可提供18-19位有效数字。 |
| wchar_t | 2 或 4 个字节 | 1 个宽字符 |
字符串
string C++的类
C风格 const char*、char*、char[]
转换
C++类型转换主要分为两种：隐式类型转换、显式类型转换（强制类型转换）。
所谓隐式类型转换，是指不需要用户干预，编译器默认进行的类型转换行为。
四种强制类型转换操作符：static_cast、const_cast、dynamic_cast、reinterpret_cast
还有类的构造方法，类的方法、流等
| 类型转换左转右 | 方法 |
|---|---|
| char->其他内置类型及const char*、char* | 隐式转换 |
| unsigned char、signed char->其他内置类型 | 隐式转换 |
| unsigned char、signed char->const char*、char* | 先转为char，再隐式转换 |
| char、unsigned char、signed char->string | 构造方法，push_back、insert等方法 |
| [signed/unsigned] [short/long] int->[signed/unsigned] char | +'0' 数值为0~9 |
| [signed/unsigned] [short/long] int->float/[long] double或[signed/unsigned] [short/long] int | 隐式转换 |
| float/[long] double -> [signed/unsigned] [short/long] int | 显示转换，否则警告(例如，warning C4244: “初始化”: 从“float”转换到“short”，可能丢失数据) |
| string->const char * | 使用string的c_str()函数 |
| string->const char *->char* | 先转const char *，再使用const_cast<char*>()转char* |
| [const] char *->string | 隐式转换 |
| const char *->char* | 使用const_cast<char*>()转char* |
| [const] char *->char[] | 使用strncpy_s()函数 |
| char* ->const char* | 隐式转换 |
注:[]表示可选，/表示或者
总结
内置类型隐式转换即可，可能丢失数据
涉及指针使用const_cast，涉及string类使用方法push_back、c_str等
建议不要使用C风格的const char *、char[]等，string不香吗？？？
string s("nkjsf");
const char* ch = s.c_str();
cout << ch << endl;
s = "efefd";
cout << ch << endl;
nkjsf
efefd
ch没有变，但是两次输出不一样。各位学完C再学C++的，字符串这里学学string吧，真的很不错。
全部代码
测试了部分，运行单个函数即可。
/*
Project:TypeConvert
Date: 2020/09/06
Author: Frank Yu
*/
#include<iostream>
#include<string>
#include<typeinfo>
using namespace std;
void display(string type,string method)
{
cout <<"转为:"<<type<< ",使用方法:" << method << endl;
}
void char2other(char c)
{
unsigned char uc = c;
display("unsigned char","隐式转换");
cout << "转换后:" << uc<<endl;
signed char sc = c;
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
int i = c;
display("int", "隐式转换");
cout << "转换后:" << i << endl;
unsigned int ui = c;
display("unsigned int", "隐式转换");
cout << "转换后:" << ui << endl;
signed int si = c;
display("signed int", "隐式转换");
cout << "转换后:" << si << endl;
unsigned short int usi = c;
display("unsigned short int", "隐式转换");
cout << "转换后:" << usi << endl;
short int s_i = c;
display("short int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = c;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = c;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = c;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = c;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = c;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = c;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = c;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1,c);
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(c);
display("string", "push_back");
cout << "转换后:" << s1 << endl;
const char* cc = &c;
display("const char*", "隐式转换");
cout << "转换后:" << cc << endl;
char* c_c = &c;
display("char*", "隐式转换");
cout << "转换后:" << c_c << endl;
}
void unsignedchar2other(unsigned char c)
{
char uc = c;
display("char", "隐式转换");
cout << "转换后:" << uc << endl;
signed char sc = c;
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
int i = c;
display("int", "隐式转换");
cout << "转换后:" << i << endl;
unsigned int ui = c;
display("unsigned int", "隐式转换");
cout << "转换后:" << ui << endl;
signed int si = c;
display("signed int", "隐式转换");
cout << "转换后:" << si << endl;
unsigned short int usi = c;
display("unsigned short int", "隐式转换");
cout << "转换后:" << usi << endl;
short int s_i = c;
display("short int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = c;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = c;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = c;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = c;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = c;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = c;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = c;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, c);
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(c);
display("string", "push_back");
cout << "转换后:" << s1 << endl;
//先转为了char，因为直接转不行(unsigned char *无法转为const char *)
char h = c;
const char* cc = &h;
display("const char*", "显示转换");
cout << "转换后:" << *cc << endl;
char* c_c = &h;
display("char*", "显示转换");
cout << "转换后:" << *c_c << endl;
}
void signedchar2other(signed char c)
{
char uc = c;
display("char", "隐式转换");
bool b = uc == c;
cout << b;
if (uc == c)cout << b;
cout << "转换后:" << uc << endl;
unsigned char sc = c;
display("unsigned char", "隐式转换");
cout << "转换后:" << sc << endl;
int i = c;
display("int", "隐式转换");
cout << "转换后:" << i << endl;
unsigned int ui = c;
display("unsigned int", "隐式转换");
cout << "转换后:" << ui << endl;
signed int si = c;
display("signed int", "隐式转换");
cout << "转换后:" << si << endl;
unsigned short int usi = c;
display("unsigned short int", "隐式转换");
cout << "转换后:" << usi << endl;
short int s_i = c;
display("short int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = c;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = c;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = c;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = c;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = c;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = c;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = c;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, c);
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(c);
display("string", "push_back");
cout << "转换后:" << s1 << endl;
//先转为了char，因为直接转不行(signed char *无法转为const char *)
char h = c;
const char* cc = &h;
display("const char*", "显示转换");
cout << "转换后:" << *cc << endl;
char* c_c = &h;
display("char*", "显示转换");
cout << "转换后:" << *c_c << endl;
}
void int2other(int i)
{
char c = i+'0';
display("int", "+'0'");
cout << "转换后:" << c << endl;
unsigned char uc = i+'0';
display("unsigned char", "隐式转换");
cout << "转换后:" << uc << endl;
signed char sc = i + '0';
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
unsigned int ui = i;
display("unsigned int", "隐式转换");
cout << "转换后:" << ui << endl;
signed int si = i;
display("signed int", "隐式转换");
cout << "转换后:" << si << endl;
unsigned short int usi = i;
display("unsigned short int", "隐式转换");
cout << "转换后:" << usi << endl;
short int s_i = i;
display("short int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = i;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = i;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = i;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = i;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = i;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = i;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = i;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, i+'0');
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(i+'0');
display("string", "push_back");
cout << "转换后:" << s1 << endl;
const char* cc = &c;
display("const char*", "隐式转换");
cout << "转换后:" << *cc << endl;
char* c_c = &c;
display("char*", "隐式转换");
cout << "转换后:" << *c_c << endl;
}
void unsignedint2other(unsigned int i)
{
char c = i + '0';
display("int", "+'0'");
cout << "转换后:" << c << endl;
unsigned char uc = i + '0';
display("unsigned char", "隐式转换");
cout << "转换后:" << uc << endl;
signed char sc = i + '0';
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
int ui = i;
display("int", "隐式转换");
cout << "转换后:" << ui << endl;
signed int si = i;
display("signed int", "隐式转换");
cout << "转换后:" << si << endl;
unsigned short int usi = i;
display("unsigned short int", "隐式转换");
cout << "转换后:" << usi << endl;
short int s_i = i;
display("short int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = i;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = i;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = i;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = i;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = i;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = i;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = i;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, i + '0');
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(i + '0');
display("string", "push_back");
cout << "转换后:" << s1 << endl;
const char* cc = &c;
display("const char*", "隐式转换");
cout << "转换后:" << *cc << endl;
char* c_c = &c;
display("char*", "隐式转换");
cout << "转换后:" << *c_c << endl;
}
void signedint2other(signed int i)
{
char c = i + '0';
display("int", "+'0'");
cout << "转换后:" << c << endl;
unsigned char uc = i + '0';
display("unsigned char", "隐式转换");
cout << "转换后:" << uc << endl;
signed char sc = i + '0';
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
int ui = i;
display("int", "隐式转换");
cout << "转换后:" << ui << endl;
unsigned int si = i;
display("unsigned int", "隐式转换");
cout << "转换后:" << si << endl;
unsigned short int usi = i;
display("unsigned short int", "隐式转换");
cout << "转换后:" << usi << endl;
short int s_i = i;
display("short int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = i;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = i;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = i;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = i;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = i;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = i;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = i;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, i + '0');
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(i + '0');
display("string", "push_back");
cout << "转换后:" << s1 << endl;
const char* cc = &c;
display("const char*", "隐式转换");
cout << "转换后:" << *cc << endl;
char* c_c = &c;
display("char*", "隐式转换");
cout << "转换后:" << *c_c << endl;
}
void shortint2other(short int i)
{
char c = i + '0';
display("int", "+'0'");
cout << "转换后:" << c << endl;
unsigned char uc = i + '0';
display("unsigned char", "隐式转换");
cout << "转换后:" << uc << endl;
signed char sc = i + '0';
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
int ui = i;
display("int", "隐式转换");
cout << "转换后:" << ui << endl;
unsigned int si = i;
display("unsigned int", "隐式转换");
cout << "转换后:" << si << endl;
unsigned short int usi = i;
display("unsigned short int", "隐式转换");
cout << "转换后:" << usi << endl;
signed int s_i = i;
display("signed int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = i;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = i;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = i;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = i;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = i;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = i;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = i;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, i + '0');
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(i + '0');
display("string", "push_back");
cout << "转换后:" << s1 << endl;
const char* cc = &c;
display("const char*", "隐式转换");
cout << "转换后:" << *cc << endl;
char* c_c = &c;
display("char*", "隐式转换");
cout << "转换后:" << *c_c << endl;
}
void unsignedshortint2other(unsigned short int i)
{
char c = i + '0';
display("int", "+'0'");
cout << "转换后:" << c << endl;
unsigned char uc = i + '0';
display("unsigned char", "隐式转换");
cout << "转换后:" << uc << endl;
signed char sc = i + '0';
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
int ui = i;
display("int", "隐式转换");
cout << "转换后:" << ui << endl;
unsigned int si = i;
display("unsigned int", "隐式转换");
cout << "转换后:" << si << endl;
short int usi = i;
display("short int", "隐式转换");
cout << "转换后:" << usi << endl;
signed int s_i = i;
display("signed int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = i;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = i;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = i;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = i;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = i;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = i;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = i;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, i + '0');
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(i + '0');
display("string", "push_back");
cout << "转换后:" << s1 << endl;
const char* cc = &c;
display("const char*", "隐式转换");
cout << "转换后:" << *cc << endl;
char* c_c = &c;
display("char*", "隐式转换");
cout << "转换后:" << *c_c << endl;
}
void signedshortint2other(signed short int i)
{
char c = i + '0';
display("int", "+'0'");
cout << "转换后:" << c << endl;
unsigned char uc = i + '0';
display("unsigned char", "隐式转换");
cout << "转换后:" << uc << endl;
signed char sc = i + '0';
display("signed char", "隐式转换");
cout << "转换后:" << sc << endl;
int ui = i;
display("int", "隐式转换");
cout << "转换后:" << ui << endl;
unsigned int si = i;
display("unsigned int", "隐式转换");
cout << "转换后:" << si << endl;
short int usi = i;
display("short int", "隐式转换");
cout << "转换后:" << usi << endl;
signed int s_i = i;
display("signed int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = i;
display("long int", "隐式转换");
cout << "转换后:" << li << endl;
signed long int sli = i;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = i;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
float f = i;
display("float", "隐式转换");
cout << "转换后:" << f << endl;
double d = i;
display("double", "隐式转换");
cout << "转换后:" << d << endl;
long double ld = i;
display("long double", "隐式转换");
cout << "转换后:" << ld << endl;
wchar_t wc = i;
display("wchar_t", "隐式转换");
cout << "转换后:" << wc << endl;
string s(1, i + '0');
display("string", "构造方法string（size_t n,char c）");
cout << "转换后:" << s << endl;
string s1;
s1.push_back(i + '0');
display("string", "push_back");
cout << "转换后:" << s1 << endl;
const char* cc = &c;
display("const char*", "隐式转换");
cout << "转换后:" << *cc << endl;
char* c_c = &c;
display("char*", "隐式转换");
cout << "转换后:" << *c_c << endl;
}
void float2int(float f)
{
int i = f;
display("int", "隐式转换");
cout << "转换后:" << i << endl;
unsigned int ui = f;
display("unsigned int", "隐式转换");
cout << "转换后:" << ui << endl;
short int si = (short int)f;
display("short int", "显式转换");
cout << "转换后:" << si << endl;
signed int s_i = f;
display("signed int", "隐式转换");
cout << "转换后:" << s_i << endl;
long int li = (long int)f;
display("long int", "显式转换");
cout << "转换后:" << li << endl;
signed long int sli = f;
display("signed long int", "隐式转换");
cout << "转换后:" << sli << endl;
unsigned long int uli = f;
display("unsigned long int", "隐式转换");
cout << "转换后:" << uli << endl;
}
void string2other(string s)
{
const char * cc;
cc = s.c_str();
display("const char *", "使用方法c_str");
cout << "转换后:" << cc << endl;
char * c = const_cast<char*>(cc);
display("char *", "c_str转为const char *,再使用const_cast<char*>()转为char *");
cout << "转换后:" << c << endl;
}
void constchar2other(const char* cc)
{
string s = cc;
display("string", "隐式转换");
cout << "转换后:" << s << endl;
char * c = const_cast<char*>(cc);
display("char *", "const_cast<char*>()");
cout << "转换后:" << c << endl;
char ca[10];
display("char[]", "strncpy_s()");
strncpy_s(ca, cc, 10);
cout << "转换后:" << ca << endl;
}
void char_2other(char* c)
{
string s = c;
display("string", "隐式转换");
cout << "转换后:" << s << endl;
const char * cc = c;
display("const char *", "隐式转换");
cout << "转换后:" << cc << endl;
char ca[10];
display("char[]", "strncpy_s()");
strncpy_s(ca, c, 10);
cout << "转换后:" << ca << endl;
}
int main()
{
//char2other('n');
unsignedchar2other('n');
//signedchar2other('n');
//signedchar2other('n');
//int2other(9);
//unsignedint2other(9);
//float2int(9.3);
//string2other("abcd");
//const char* cc = "abcd";
//constchar2other("abcd");
//char_2other("sdfesgrf");
//问题1 ch会变
//string s("nkjsf");
//const char* ch = s.c_str();
//cout << ch << endl;
//s = "efefd";
//cout << ch << endl;
//问题2 char2other函数输出cc没有烫 unsignedchar2other输出cc有烫
//char c = 'n';
//const char *cc = &c;
//cout << cc << endl;
}
