g ++预处理器输出

Question

我想只获得预处理版本file.cc.我做了g++ -E file.cc,得到了:

# 1 "file.cc"
# 1 "<command-line>"
# 1 "file.cc"

我做错了什么？

Answer 1

假设您的源文件包含一个简单的main函数:

$ cat file.cc
int main() {
    return 0;
}

然后,使用您显示的命令,输出如下所示:

$ g++ -E file.cc
# 1 "file.cc"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "file.cc"

int main() {
    return 0;
}

问题中显示的输出在file.cc空时发生.请注意,"empty"表示文件仍然可以包含注释或#ifdef具有计算结果为false的条件的块 - 因为预处理器将它们过滤掉,它们也不会出现在输出中.

Answer 2

如果您不想使用行标记,请使用-P选项:

-P
    Inhibit generation of linemarkers in the output from the preprocessor. This might
    be useful when running the preprocessor on something that is not C code, and will
    be sent to a program which might be confused by the linemarkers.