我正在寻找关于基本c++类型大小的详细信息。 我知道这取决于架构(16位、32位、64位)和编译器。
但是c++有标准吗?
我在32位架构上使用Visual Studio 2008。以下是我得到的答案:
char : 1 byte
short : 2 bytes
int : 4 bytes
long : 4 bytes
float : 4 bytes
double: 8 bytes
我试图在不同的架构和编译器下找到char、short、int、long、double、float(以及其他我没有想到的类型)的大小的可靠信息，但没有多大成功。
当前回答
c++标准是这样说的:
3.9.1,§2:
There are five signed integer types : "signed char", "short int", "int", "long int", and "long long int". In this list, each type provides at least as much storage as those preceding it in the list. Plain ints have the natural size suggested by the architecture of the execution environment (44); the other signed integer types are provided to meet special needs. (44) that is, large enough to contain any value in the range of INT_MIN and INT_MAX, as defined in the header <climits>.
结论:这取决于您使用的是哪种体系结构。其他任何假设都是错误的。
其他回答
unsigned char bits = sizeof(X) << 3;
其中X是char,int,long等。会得到X的比特大小。
根据大小有四种类型的整数:
短整数:2字节 长整数:4字节 Long Long integer: 8字节 整数:取决于编译器(16位、32位或64位)
你可以使用:
cout << "size of datatype = " << sizeof(datatype) << endl;
Datatype = int, long int等。 您将能够看到您键入的任何数据类型的大小。
不，字体大小没有标准。标准只要求:
sizeof(short int) <= sizeof(int) <= sizeof(long int)
如果你想要一个固定大小的变量，你能做的最好的事情就是像这样使用宏:
#ifdef SYSTEM_X
#define WORD int
#else
#define WORD long int
#endif
然后可以使用WORD定义变量。不是说我喜欢这个，而是说这是最方便的方式。
正如其他人回答的那样，“标准”都将大部分细节保留为“实现定义的”，只声明类型“char”的宽度至少为“char_bis”，并且“char <= short <= int <= long <= long long”(浮点数和双精度浮点数与IEEE浮点标准基本一致，长双精度浮点数通常与双精度浮点数相同——但在更当前的实现中可能更大)。
Part of the reasons for not having very specific and exact values is because languages like C/C++ were designed to be portable to a large number of hardware platforms--Including computer systems in which the "char" word-size may be 4-bits or 7-bits, or even some value other than the "8-/16-/32-/64-bit" computers the average home computer user is exposed to. (Word-size here meaning how many bits wide the system normally operates on--Again, it's not always 8-bits as home computer users may expect.)
If you really need a object (in the sense of a series of bits representing an integral value) of a specific number of bits, most compilers have some method of specifying that; But it's generally not portable, even between compilers made by the ame company but for different platforms. Some standards and practices (especially limits.h and the like) are common enough that most compilers will have support for determining at the best-fit type for a specific range of values, but not the number of bits used. (That is, if you know you need to hold values between 0 and 127, you can determine that your compiler supports an "int8" type of 8-bits which will be large enought to hold the full range desired, but not something like an "int7" type which would be an exact match for 7-bits.)
注意:使用了许多Un*x源包”。/configure”脚本，它将探测编译器/系统的功能，并输出一个合适的Makefile和config.h。您可以检查其中一些脚本，看看它们是如何工作的，以及它们如何探测编译器/系统功能，并遵循它们的指导。
