c——内置类型字面值

布尔型

• true
• false

void bool_literals(){    bool b1 = true;    bool b2 = false;}

注：bool不是c内置类型，bool，true，false不是c关键字，需#include<stdbool.h>

#ifndef __STDBOOL_H#define __STDBOOL_H/* Don't define bool, true, and false in C++, except as a GNU extension. */#ifndef __cplusplus#define bool _Bool#define true 1#define false 0#elif defined(__GNUC__) && !defined(__STRICT_ANSI__)/* Define _Bool, bool, false, true as a GNU extension. */#define _Bool bool#define bool  bool#define false false#define true  true#endif#define __bool_true_false_are_defined 1#endif /* __STDBOOL_H */

注：_Bool是c内置类型，是c关键字，无需#include<stdbool.h>，bool，true，false只是宏而已

字面值类型

void bool_type_check(){    printf("sizeof(true) = %ld, sizeof(false) = %ld\n", sizeof(true), sizeof(false));    printf("true = %d, false = %d\n", true, false);}

output：

sizeof(true) = 4, sizeof(false) = 4true = 1, false = 0

结论：

• true和false为int字面值

字符型

• 字符：'a'
• 转义字符：'\n'，’\"‘，'\123'，'\x6b'

void char_literals(){    char c1 = '\a';    char c2 = '\n';    char c3 = '\"';    char c4 = '\123';    char c5 = '\x6b';        wchar_t wc1 = L'a';    wchar_t wc2 = L'\n';    wchar_t wc3 = L'\"';    wchar_t wc4 = L'\123';    wchar_t wc5 = L'\x6b';}

注：前缀L表示wchar_t类型(宽字符)

字面值类型

void type_check(char){    cout << "char" << endl;}void type_check(signed char){    cout << "signed char" << endl;}void type_check(unsigned char){    cout << "unsigned char" << endl;}void type_check(wchar_t){    cout << "wchar_t" << endl;}void char_type_check(){    type_check('a');    type_check(L'a');}

output：

charwchar_t

结论：

• char，signed char，unsigned char是不同类型
• 字符字面值为char类型

整型

格式表示：

• 十进制：123，456
• 八进制：0123，0456
• 十六进制：0x7abc，0X8def

取值范围：

• 8 bits signed：[-128, 127]([-2^7,  2^7 - 1])；8 bits unsigned：[0, 255]([0, 2^8 - 1])
• 16 bits signed：[-32768, 32767]([-2^15 ~ 2^15 - 1])；16 bits unsigned：[0, 65535]([0, 2^16 - 1])
• 32 bits signed：[-2147483648, 2147483647]([-2^31, 2^31 - 1])；32 bits unsigned：[0, 4294967295]([0, 2^32 - 1])
• 64 bits signed：[-9223372036854775808, 9223372036854775807]([-2^63, 2^63 - 1])；64 bits unsigned：[0, 18446744073709551615]([0, 2^64 - 1])

字面值后缀：

• u或U：unsigned
• l或L：long
• ll或LL：long long，不能用Ll或lL表示

注：后缀可以组合使用，例如UL或LU——unsigned long，l和1易混淆，用L表示

void int_literals(){    int i1 = 123;    int i2 = 0456;    int i3 = 0x7abc;    int i4 = 0X8def;    unsigned int ui = 123U;    long l = 123L;    unsigned long ul = 123LU;    long long ll = 123LL;    unsigned long long ull = 123ULL;}

字面值类型

void type_check(signed int){    cout << "signed int" << endl;}void type_check(unsigned int){    cout << "unsigned int" << endl;}void type_check(signed long){    cout << "signed long" << endl;}void type_check(unsigned long){    cout << "unsigned long" << endl;}void type_check(signed long long){    cout << "signed long long" << endl;}void type_check(unsigned long long){    cout << "unsigned long long" << endl;}void int_type_check(){    cout << "-----sizeof-----" << endl;    cout << "sizeof(int) = " << sizeof(int) << endl;    cout << "sizeof(long) = " << sizeof(long) << endl;    cout << "sizeof(long long) = " << sizeof(long long) << endl;        cout << "-----int-----" << endl;    type_check(5);    type_check(-2147483648);//32位int取值下限    type_check(2147483647);//32位int取值上限    type_check(-2147483649);//32位int取值下限-1    type_check(2147483648);//32位int取值上限+1        cout << "-----long-----" << endl;    type_check(-9223372036854775808);//64位long取值下限    type_check(9223372036854775807);//64位long取值上限    type_check(-9223372036854775809);//64位long取值下限-1    type_check(9223372036854775808);//64位long取值上限+1}

output：

-----sizeof-----sizeof(int) = 4sizeof(long) = 8sizeof(long long) = 8-----int-----signed intsigned longsigned intsigned longsigned long-----long-----unsigned long longsigned longunsigned long longunsigned long long

结论：

• 正整数类型匹配按取值范围以int->long->long long顺序匹配，如果还不能匹配，最后考虑匹配unsigned long long，因此unsigned long long是最后匹配项
• 负号(-)本质是运算负号，取补码运算，因此负整数的类型是其对应正整数的类型

浮点型

格式表示：

• 十进制(必须包含小数点)：123.456，.123，123.
• 科学计数法(e或E前后必须有值)：123e3，4.56E6，.789e9

字面值后缀：

• f或F：float
• l或L：long double

注：l和1易混淆，用L表示

void float_literals(){    float f1 = 123.456f;    float f2 = .123e3f;        double d1 = 123.456;    double d2 = .123e3;        long double ld1 = 123.456L;    long double ld2 = .123e3L;}

字面值类型

void type_check(float){    cout << "float" << endl;}void type_check(double){    cout << "double" << endl;}void type_check(long double){    cout << "long double" << endl;}void float_type_check(){    type_check(123.456);    type_check(.123e3);}

output：

doubledouble

结论：

• 浮点字面值为double类型