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。
有一个标准,它是在各种标准文档(ISO, ANSI等)中指定的。
维基百科有一个很好的页面解释了各种类型和它们可以存储的最大值:
计算机科学中的整数。
然而,即使使用标准的c++编译器,您也可以使用以下代码片段相对容易地找到:
#include <iostream>
#include <limits>
int main() {
// Change the template parameter to the various different types.
std::cout << std::numeric_limits<int>::max() << std::endl;
}
std::numeric_limits的文档可以在Roguewave上找到。它包含大量其他命令,您可以调用这些命令来查找各种限制。这可以用于任何传递大小的任意类型,例如std::streamsize。
约翰的回答包含了最好的描述,因为那些肯定是成立的。不管你在什么平台上,有另一个很好的页面详细介绍了每种类型必须包含多少位:int类型,这是在标准中定义的。
我希望这能有所帮助!
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。