I am trying to figure out what version of Boost my code thinks it's using. I want to do something like this:
#error BOOST_VERSION
but the preprocessor does not expand BOOST_VERSION.
I know I could print it out at run-time from the program, and I know I could look at the output of the preprocessor to find the answer. I feel like having a way of doing this during compilation could be useful.
This question is related to
macros
c-preprocessor
boost-preprocessor
Take a look at the Boost documentation as well, regarding how you are using the macro:
In reference to BOOST_VERSION, from http://www.boost.org/doc/libs/1_37_0/libs/config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.boost_helper_macros:
Describes the boost version number in XXYYZZ format such that:
(BOOST_VERSION % 100)is the sub-minor version,((BOOST_VERSION / 100) %1000)is the minor version, and(BOOST_VERSION / 100000)is the major version.
You could write a program that prints out BOOST_VERSION and compile and run it as part of your build system. Otherwise, I think you're out of luck.
BOOST_PP_STRINGIZE seems a excellent solution for C++, but not for regular C.
Here is my solution for GNU CPP:
/* Some test definition here */
#define DEFINED_BUT_NO_VALUE
#define DEFINED_INT 3
#define DEFINED_STR "ABC"
/* definition to expand macro then apply to pragma message */
#define VALUE_TO_STRING(x) #x
#define VALUE(x) VALUE_TO_STRING(x)
#define VAR_NAME_VALUE(var) #var "=" VALUE(var)
/* Some example here */
#pragma message(VAR_NAME_VALUE(NOT_DEFINED))
#pragma message(VAR_NAME_VALUE(DEFINED_BUT_NO_VALUE))
#pragma message(VAR_NAME_VALUE(DEFINED_INT))
#pragma message(VAR_NAME_VALUE(DEFINED_STR))
Above definitions result in:
test.c:10:9: note: #pragma message: NOT_DEFINED=NOT_DEFINED
test.c:11:9: note: #pragma message: DEFINED_BUT_NO_VALUE=
test.c:12:9: note: #pragma message: DEFINED_INT=3
test.c:13:9: note: #pragma message: DEFINED_STR="ABC"
For "defined as interger", "defined as string", and "defined but no value" variables , they work just fine. Only for "not defined" variable, they displayed exactly the same as original variable name. You have to used to it -- or maybe someone can provide a better solution.
BOOST_VERSION is defined in the boost header file version.hpp.
#define a <::BOOST_VERSION>
#include a
MSVC2015: fatal error C1083: Cannot open include file: '::106200': No such file or directory
Works even if preprocess to file is enabled, even if invalid tokens are present:
#define a <::'*/`#>
#include a
MSVC2015: fatal error C1083: Cannot open include file: '::'*/`#': No such file or directory
GCC4.x: warning: missing terminating ' character [-Winvalid-pp-token]
#define a <::'*/`#>
You could also preprocess the source file and see what the preprocessor value evaluates to.
If you are using Visual C++, you can use #pragma message:
#include <boost/preprocessor/stringize.hpp>
#pragma message("BOOST_VERSION=" BOOST_PP_STRINGIZE(BOOST_VERSION))
Edit: Thanks to LB for link
Apparently, the GCC equivalent is (not tested):
#pragma message "BOOST_VERSION=" BOOST_PP_STRINGIZE(BOOST_VERSION)
Instead of #error, try redefining the macro, just before it is being used. Compilation will fail and compiler will provide the current value it thinks applies to the macro.
#define BOOST_VERSION blah
Without boost :
define same macro again and compiler HIMSELF will give warning.
From warning you can see location of the previous definition.
vi file of previous definition .
ambarish@axiom:~/cpp$ g++ shiftOper.cpp
shiftOper.cpp:7:1: warning: "LINUX_VERSION_CODE" redefined
shiftOper.cpp:6:1: warning: this is the location of the previous definition
#define LINUX_VERSION_CODE 265216
#define LINUX_VERSION_CODE 666
int main ()
{
}
Looking at the output of the preprocessor is the closest thing to the answer you ask for.
I know you've excluded that (and other ways), but I'm not sure why. You have a specific enough problem to solve, but you have not explained why any of the "normal" methods don't work well for you.
As far as I know '#error' only will print strings, in fact you don't even need to use quotes.
Have you tried writing various purposefully incorrect code using "BOOST_VERSION"? Perhaps something like "blah[BOOST_VERSION] = foo;" will tell you something like "string literal 1.2.1 cannot be used as an array address". It won't be a pretty error message, but at least it'll show you the relevant value. You can play around until you find a compile error that does tell you the value.
Are you looking for
#if BOOST_VERSION != "1.2"
#error "Bad version"
#endif
Not great if BOOST_VERSION is a string, like I've assumed, but there may also be individual integers defined for the major, minor and revision numbers.
In Microsoft C/C++, you can use the built-in _CRT_STRINGIZE() to print constants. Many of my stdafx.h files contain some combination of these:
#pragma message("_MSC_VER is " _CRT_STRINGIZE(_MSC_VER))
#pragma message("_MFC_VER is " _CRT_STRINGIZE(_MFC_VER))
#pragma message("_ATL_VER is " _CRT_STRINGIZE(_ATL_VER))
#pragma message("WINVER is " _CRT_STRINGIZE(WINVER))
#pragma message("_WIN32_WINNT is " _CRT_STRINGIZE(_WIN32_WINNT))
#pragma message("_WIN32_IE is " _CRT_STRINGIZE(_WIN32_IE))
#pragma message("NTDDI_VERSION is " _CRT_STRINGIZE(NTDDI_VERSION))
and outputs something like this:
_MSC_VER is 1915
_MFC_VER is 0x0E00
_ATL_VER is 0x0E00
WINVER is 0x0600
_WIN32_WINNT is 0x0600
_WIN32_IE is 0x0700
NTDDI_VERSION is 0x06000000
Source: Stackoverflow.com