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重识C++ 基本类型及其转换 类型 占字节 别名 表示范围 int 4 signed –2,147,483,648 to 2,147,483,647 unsigned int 4 unsigned 0 to 4,294,967,295 __int8 1 char –128 to 127 unsigned __int8 1 unsigned char 0 to 255 __int16 2 short, short int, signed short int –32,768 to 32,767 unsigned __int16 2 unsigned short, unsigned short int 0 to 65,535 __int32 4 signed, signed int, int –2,147,483,648 to 2,147,483,647 unsigned __int32 4 unsigned, unsigned int 0 to 4,294,967,295 __int64 8 long long, signed long long –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 unsigned __int64 8 unsigned long long 0 to 18,446,744,073,709,551,615 bool 1 none false or true char 1 none –128 to 127 signed char 1 none –128 to 127 unsigned char 1 none 0 to 255 short 2 short int, signed short int –32,768 to 32,767 unsigned short 2 unsigned short int 0 to 65,535 long 4 long int, signed long int –2,147,483,648 to 2,147,483,647 unsigned long 4 unsigned long int 0 to 4,294,967,295 long long 8 none (but equivalent to __int64) –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 unsigned long long 8 none (but equivalent to unsigned __int64) 0 to 18,446,744,073,709,551,615 enum varies none float 4 none 3.4E +/- 38 (7 digits) double 8 none 1.7E +/- 308 (15 digits) long double same as double none Same as double wchar_t 2 __wchar_t 0 to 65,535
#include <iostream> using namespace std; template<typename T1,typename T2> void explicit_cast() { T1 s1,d2; T2 d1,s2; cin>>s1>>s2>>d1>>d2; cout<<"T1:"<<typeid(T1).name()<<" T2:"<<typeid(T2).name()<<endl; d1=(T2)s1; d2=(T1)s2; cout<<d1<<d2<<endl; } #define all_cast1(x,y) \ {\ explicit_cast<x,y>();\ explicit_cast<unsigned x,y>();\ explicit_cast<x,unsigned y>();\ explicit_cast<unsigned x,unsigned y>();\ } #define all_cast2(x,y) \ {\ explicit_cast<x,y>();\ explicit_cast<unsigned x,y>();\ } void main() { all_cast1(char,char); all_cast1(char,short); all_cast1(char,int); all_cast1(char,long long); all_cast2(char,float); all_cast2(char,double); all_cast1(short,short); all_cast1(short,int); all_cast1(short,long long); all_cast2(short,float); all_cast2(short,double); all_cast1(int,int); all_cast1(int,long long); all_cast2(int,float); all_cast2(int,double); all_cast1(long long,long long); all_cast2(long long,float); all_cast2(long long,double); explicit_cast<float,float>(); explicit_cast<float,double>(); explicit_cast<double,double>(); } 复制代码 转换前T1
1字节整形(char,bool,__int8) 2字节整形(short,__int16) 4字节整形(int,__int32,long) 8字节整形(__int64,long long) 4字节浮点(float) 8字节浮点(double,long double) 1字节整形(char,bool,__int8) s->s mov s->s mov s->s mov s->s mov s->s cvttss2si s->s cvttsd2si 2字节整形(short,__int16) s->s movsx s->s mov s->s mov s->s mov s->s cvttss2si s->s cvttsd2si 4字节整形(int,__int32,long) s->s movsx cdq s->s movsx s->s mov s->s mov s->s cvttss2si s->s cvttsd2si 8字节整形(__int64,long long) s->s movsx cdq s->s movsx cdq s->s mov cdq s->s mov s->s fld s->s fld 4字节浮点(float) s->s movsx s->s movsx s->s cvtsi2ss s->s fild fstp movss cvtsd2ss 8字节浮点(double,long double) s->s movsx s->s movsx s->s cvtsi2sd s->s fild fstp cvtss2sd movsd
由于是debug版本，所以指令较多 ②float s2;unsigned int d2=(unsignd int)s2; ③Unsigned int s1;doublet d1=(double)s1; ④double s2;unsigned int d2=(unsigned int)s2; ⑤Unsigned long long s1;doublet d1=(double)s1; ⑥double s2;unsigned long long d2=(unsigned long long)s2; #include <iostream> using namespace std; template<typename T> void assignment() { cout<<"T:"<<typeid(T).name()<<endl; //初始化 T s1=0,s2=1; //赋值 s1=1; s2=0; } #define all_assign(x) \ {\ assignment<x>();\ assignment<unsigned x>();\ } void main() { all_assign(char); assignment<bool>(); all_assign(__int8); all_assign(short); all_assign(__int16); all_assign(int); all_assign(__int32); all_assign(long); all_assign(long long); all_assign(__int64); assignment<float>(); assignment<double>(); assignment<long double>(); } 复制代码 1/2/4字节整形 8字节整形 4字节浮点 8字节浮点 赋值为零 mov xorpd movlpd movss movsd 赋值为非零 mov mov movss movsd
对于结构体memset方式清零，通常会优化为各个成员清零
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