[C++]cpp小笔记3 --- C++基础类型的大小和转换

最新推荐文章于 2022-11-07 17:00:52 发布

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最新推荐文章于 2022-11-07 17:00:52 发布

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本文介绍了C++中不同整数类型（如short、int、long等）的大小，并通过示例展示了如何使用sizeof关键字来获取变量的大小。此外，还讲解了climits头文件中的常量值以及无符号类型和类型转换的概念。

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1. 类型的大小

A short integer is at least 16 bits wide.
An int integer is at least as big as short.
A long integer is at least 32 bits wide and at least as big as int.
A long long integer is at least 64 bits wide and at least as big as long.

2. sizeof and climits

int days = 0
cout << "size of days is " << sizeof(days) << endl;
cout << "size of int is " << sizeof(int) << endl;

Results:
size of days is 4
size of int is 4

climits中定义了c++中基础类型的最大值，最小值，大小的常量值。

CHAR_BIT          Number of bits in a char
CHAR_MAX       Maximum char value
CHAR_MIN        Minimum char value
SCHAR_MAX    Maximum signed char value
SCHAR_MIN     Minimum signed char value
UCHAR_MAX   Maximum unsigned char value
SHRT_MAX       Maximum short value
SHRT_MIN        Minimum short value
USHRT_MAX    Maximum unsigned short value

climits的使用

#include <climits>
// use limits.h for older systems

3. 无符号类型

unsigned short change;
unsigned int rovert;
unsigned quarterback;  //unsigned int type
unsigned long gone;
unsigned long long lang_lang;

从这张图上可以看出

If signed integer max value is 32767. 32767 + 1, result is -32768.

If unsigned integer max value is 65535, if 65535 + 1, result is 0.

4. 类型转换。

自动类型转换：

C++会自动将converts bool, char, unsigned char, signed char, and short values to int.
The unsigned short type is converted to int if short is smaller than int. If the two types are the same size, unsigned short is con-
verted to unsigned int. This rule ensures that there’s no data loss in promoting unsigned short.
When an operation involves two types, the smaller is converted to the larger.

强制转换：

int a = 0;
double b = (double)a; 

OR 

double b = double(a);

double b = static_cast<double> (a);