base之basictypes.h基本数据类型 (1)

定义了基本的数据类型，比如int8, int16, int32以及基本数据类型的范围

关键在于数据类型占多少字节，比如char占1个字节，int占4个字节。

至于int, long，这两个我就不清楚，原本以为64位系统下，int占4个字节，long占8个字节。

实际上64位下，int和long都是占4字节

类型	64位系统下所占字节数
int	4
long	4
long int	4
long long	8
long long int	8

也就是说long long和long long int等同，因为占的字节数一样，表示的范围也一样,表示如下表

类型	同类型	64位系统下所占字节数
short	short int	2
int	int	4
long	long int	4
long long	long long int	8

其实stdint.h是这么实现的

/* Exact integral types.  */

/* Signed.  */

/* There is some amount of overlap with <sys/types.h> as known by inet code */
#ifndef __int8_t_defined
# define __int8_t_defined
typedef signed char     int8_t;
typedef short int       int16_t;
typedef int         int32_t;
# if __WORDSIZE == 64
typedef long int        int64_t;
# else
__extension__
typedef long long int       int64_t;
# endif
#endif

最后贴上我的代码

#ifndef _BASE_BASICTYPES_H_
#define _BASE_BASICTYPES_H_

//
// signed
//
typedef signed char     schar;

typedef signed char     int8;

typedef signed short    int16;

typedef signed int      int32;

typedef signed long long    int64;

//
// unsigned
//
typedef unsigned char   uchar;

typedef unsigned char   uint8;

typedef unsigned short  uint16;

typedef unsigned int    uint32;

typedef unsigned long long  uint64;

#endif // _BASE_BASICTYPES_H_

测试代码

#include "gtest/gtest.h"
#include "base/basictypes.h"

TEST(basictypes_unittest, size)
{
EXPECT_EQ(sizeof(schar), 1);
EXPECT_EQ(sizeof(int8),  1);
EXPECT_EQ(sizeof(int16), 2);
EXPECT_EQ(sizeof(int32), 4);
EXPECT_EQ(sizeof(int64), 8);

EXPECT_EQ(sizeof(uchar), 1);
EXPECT_EQ(sizeof(uint8), 1);
EXPECT_EQ(sizeof(uint16), 2);
EXPECT_EQ(sizeof(uint32), 4);
EXPECT_EQ(sizeof(uint64), 8);
}

简单实现一遍chromium的base，增长见识

源码 chromium-4.0.210.0_p26329

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