[英]Define global const variables known at run-time with helper functions (c++)
I want to define a series of global variables from within a parametrise() helper function like this: 我想从如下的parametrise()帮助函数中定义一系列全局变量:
// helper.h
namespace settings {
extern const unsigned short something;
}
namespace helper {
void parametrise(int, char**); // parametrise from command line using boost::program_options
}
// main.cpp
int main( int argc, char** argv) {
helper::parametrise(argc, argv);
return 0;
}
// helper.cpp
void helper::parametrise(int, char**) {
// parse input here
const unsigned short settings::something = .. // this is what I want to do
}
This code does not compile of course, but there has to be a way around it.. or not? 该代码当然不会编译,但是必须有一种解决方法。
You can make it writable only within that translation unit, and have it externally const, like so: 您可以使其仅在该翻译单元内可写,并使其在外部const内,如下所示:
// helper.h
namespace settings {
extern const unsigned short& something;
}
void parametrise(int, char**);
// helper.cpp
namespace { namespace settings_internal {
unsigned short something;
}}
namespace settings {
const unsigned short& something = settings_internal::something;
}
void parametrise(int, char**) { settings_internal::something = 123; }
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