Casting (converting) number in a format with multiple dots (a version number) to string

Question

#define EXTERNAL_API_VERSION 1.12.1
std::string version = boost::lexical_cast<std::string>(EXTERNAL_API_VERSION);

This code generates a compilation error:

error C2143: syntax error : missing ')' before 'constant'
error C2059: syntax error : ')'

Are there any simple alternatives for casting number in such format (more then one dot) to string?

It's not a valid lexeme in C++, so no it's not possible. The only way to have versions in code is as strings. — Some programmer dude, Oct 15 '13 at 14:04
@PaperBirdMaster you are right, but i have to cast it to string :-) — Sanich, Oct 15 '13 at 14:05
What's wrong with `const char* EXTERNAL_API_VERSION = "1.12.1";`? — juanchopanza, Oct 15 '13 at 14:07
@JoachimPileborg The define {EXTERNAL_API_VERSION} is defined in external API. Can't touch that code. — Sanich, Oct 15 '13 at 14:09
@juanchopanza and what's wrong with `const std::string EXTERNAL_API_VERSION("1.12.1");` ;) — PaperBirdMaster, Oct 15 '13 at 14:11
Whose idea was it to define `EXTERNAL_API_VERSION` that way? This question seems to be the only Google hit for that identifier. BTW, I believe it's a valid token sequence: a floating-point constant `1.12`, followed by `.`, followed by an integer constant `1`. That sequence can't appear after preprocessing in a syntactically valid program, though ([you can't overload `.`](http://stackoverflow.com/q/520035/827263)), so that doesn't do you much good. — Keith Thompson, Oct 22 '13 at 23:25

masoud · Accepted Answer · 2013-12-07T22:32:12.470

5

Without touching EXTERNAL_API_VERSION, you need to expand that marco in two levels to a string literal:

#define S(X) #X
#define STR(X) S(X)

std::string version = STR(EXTERNAL_API_VERSION);

edited Dec 07 '13 at 22:32

answered Oct 15 '13 at 14:09

masoud

1

@Sanich: In first step you expand `EXTERNAL_API_VERSION` to `1.12.1`, in the next step you make it a string literal by `#`, `"1.12.1"`. You can not mix these two step in one. It's useful to read [this](http://stackoverflow.com/a/19343239/952747) – masoud Oct 16 '13 at 11:25

1 Answers1