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C++ 速查手冊 V1.00 - 單元 3.3 - 整數




整數利用三個關鍵字 shortintlong 進行宣告,另可與 signedunsigned 兩個修飾詞搭配,如下表


short short int signed short signed short int
unsigned short unsigned short int
int signed signed int
unsigned unsigned int
long long int signed long signed long int
unsigned long unsigned long int
long long long long int signed long long signed long long int
unsigned long long unsigned long long int

通常 shortint 至少是 16 位元, long 至少為 32 位元,而 long long 至少為 64 位元 ,視所用機器及編譯器而定。 signed 表示帶正負號, unsigned 表示不帶正負號,這是說 unsigned 的值為 0 或正整數。


long long 為 C++11 新增的資料型態。

以下程式計算出各種宣告組合在 64 位元機器所佔的位元組數


001 #include <iostream>
002
003 int main() {
004    std::cout << "short : "
005              << sizeof(short
006              << std::endl;
007    std::cout << "short int : "
008              << sizeof(short int)
009              << std::endl;
010    std::cout << "signed short : "
011              << sizeof(signed short)
012              << std::endl;
013    std::cout << "signed short int : "
014              << sizeof(signed short int)
015              << std::endl;
016    std::cout << "unsigned short : "
017              << sizeof(unsigned short)
018              << std::endl;
019    std::cout << "unsigned short int : "
020              << sizeof(unsigned short int)
021              << std::endl;
022    std::cout << "int : "
023              << sizeof(int)
024              << std::endl;
025    std::cout << "signed : "
026              << sizeof(signed)
027              << std::endl;
028    std::cout << "signed int : "
029              << sizeof(signed int)
030              << std::endl;
031    std::cout << "unsigned : "
032              << sizeof(unsigned)
033              << std::endl;
034    std::cout << "unsigned int : "
035              << sizeof(unsigned int)
036              << std::endl;
037    std::cout << "long : "
038              << sizeof(long)
039              << std::endl;
040    std::cout << "long int : "
041              << sizeof(long int)
042              << std::endl;
043    std::cout << "signed long : "
044              << sizeof(signed long)
045              << std::endl;
046    std::cout << "signed long int : "
047              << sizeof(signed long int)
048              << std::endl;
049    std::cout << "unsigned long : "
050              << sizeof(unsigned long)
051              << std::endl;
052    std::cout << "unsigned long int : "
053              << sizeof(unsigned long int)
054              << std::endl;
055    std::cout << "long long : "
056              << sizeof(long long)
057              << std::endl;
058    std::cout << "long long int : "
059              << sizeof(long long int)
060              << std::endl;
061    std::cout << "signed long long : "
062              << sizeof(signed long long)
063              << std::endl;
064    std::cout << "signed long long int: "
065              << sizeof(signed long long int)
066              << std::endl;
067    std::cout << "unsigned long long : "
068              << sizeof(unsigned long long)
069              << std::endl;
070    std::cout << "unsigned long long int: "
071              << sizeof(unsigned long long int)
072              << std::endl;
073
074    return 0;
075
076    
077 /* Kaiching Chang
078    u0303.cpp
079    2014-02 */

編譯後執行,結果如下


$ g++ u0303.cpp
$ ./a.out
short : 2
short int : 2
signed short : 2
signed short int : 2
unsigned short : 2
unsigned short int : 2
int : 4
signed : 4
signed int : 4
unsigned : 4
unsigned int : 4
long : 8
long int : 8
signed long : 8
signed long int : 8
unsigned long : 8
unsigned long int : 8
long long : 8
long long int : 8
signed long long : 8
signed long long int: 8
unsigned long long : 8
unsigned long long int: 8
$

continue ...

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