[英]What is <built-in> in C++ preprocessor output?
Summary : C++ preprocessor output includes some lines that say <built-in>
. 简介 :C ++预处理器输出包含一些说明
<built-in>
。 I'm curious to know what these are for. 我很想知道它们的用途。
Details : 细节 :
When I compile the following code in a file named test.cpp
with clang++ -E
(output from g++
is similar): 当我在一个名为
test.cpp
的文件中使用clang++ -E
编译以下代码时( g++
输出类似):
#include <iostream>
int main()
{
std::cout << "Hello World!" << std::endl;
return 0;
}
the first few lines of output are as follows: 前几行输出如下:
# 1 "test.cpp"
#1“test.cpp”
# 1 "test.cpp" 1#1“test.cpp”1
# 1 "<built-in>" 1#1“<内置>”1
# 1 "<built-in>" 3#1“<内置>”3
# 156 "<built-in>" 3#156“<内置>”3
# 1 "<command line>" 1#1“<命令行>”1
# 1 "<built-in>" 2#1“<内置>”2
# 1 "test.cpp" 2#1“test.cpp”2
My question is what do the <built-in>
statements mean. 我的问题是
<built-in>
语句是什么意思。
A macro expands to "1", and in case of built-in, the macro is defined by default, eg, __cplusplus
, in case of command line, the macro is defined on the command-line, ie, -DMACRO=1
. 宏扩展为“1”,并且在内置的情况下,宏默认定义,例如
__cplusplus
,在命令行的情况下,宏在命令行上定义,即-DMACRO=1
。
You can see a list of predefined macros: 您可以看到预定义宏的列表:
cpp -dM foo.h
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