How to make preprocessor generate a string for __LINE__ keyword?
__FILE__
is replaced with "MyFile.cpp" by C++ preprocessor.
I want __LINE__
to be replaced with "256" string not with 256 integer.
Without using my own written functions like
toString(__LINE__);
Is that possible? How can I do it?
VS 2008
EDIT I'd like to automatically F开发者_运维技巧ind and Replace all throw;
statements with
throw std::runtime_error(std::string("exception at ") + __FILE__ + " "+__LINE__);
in my sources. If I use macro or function to convert __LINE__
into a string I'll need to modify each source file manually.
You need the double expansion trick:
#define S(x) #x
#define S_(x) S(x)
#define S__LINE__ S_(__LINE__)
/* use S__LINE__ instead of __LINE__ */
Addendum, years later: It is a good idea to go a little out of one's way to avoid operations that may allocate memory in exception-handling paths. Given the above, you should be able to write
throw std::runtime_error("exception at " __FILE__ " " S__LINE__);
which will do the string concatenation at compile time instead of runtime. It will still construct a std::string (implicitly) at runtime, but that's unavoidable.
EDIT: In response to request on the other answer, I added a non-macro version:
#include <iostream>
#include <boost/lexical_cast.hpp>
#include <string>
#define B(x) #x
#define A(x) B(x)
void f(const char *s) {
std::cout << s << "\n";
}
int main() {
f(A(__LINE__));
f(boost::lexical_cast<std::string>(__LINE__).c_str());
}
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