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IDProjectCategoryView StatusDate SubmittedLast Update
0015777CMakeCMakepublic2015-10-08 06:062015-10-08 11:14
ReporterFrancis ANDRE 
Assigned To 
PriorityhighSeverityfeatureReproducibilityalways
StatusclosedResolutionno change required 
PlatformOSOS Version
Product VersionCMake 3.3.1 
Target VersionFixed in Version 
Summary0015777: The define constant _DEBUG should be defined implicitly when target build is Debug
DescriptionHi

As the constant NDEBUG is implicitly defined for a Release build, the constant _DEBUG should be also implicitly defined for a Debug build.

Currently, implicit constant are define as below:

-- CMAKE_CXX_FLAGS_DEBUG:=-g
-- CMAKE_CXX_FLAGS_RELEASE:=-O3 -DNDEBUG
-- CMAKE_CXX_FLAGS_MINSIZEREL:=-Os -DNDEBUG
-- CMAKE_CXX_FLAGS_RELWITHDEBINFO:=-O2 -g -DNDEBUG
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  Notes
(0039531)
Nils Gladitz (developer)
2015-10-08 06:25

 NDEBUG is defined by the C/C++ standards; _DEBUG is not.

_DEBUG is used in the context of Microsoft (and compatible) compilers where it indicates that a debug runtime is being used.

CMake does set _DEBUG in that context.

For other compilers the _DEBUG macro has no standard defined semantics.
(0039532)
Alex Turbov (reporter)
2015-10-08 06:28

 No! It shouldn't!
NDEBUG is a "standard" macro which must be defined to eliminate assert() calls.
While _DEBUG (as for me) usually defined by newbies... For example what kind of build you'll get if neither NDEBUG nor _DEBUG are defined? Or both are defined? -- in your code you should handle all that combinations (because user may bring his compile options while build your project)... that makes your code ugly...

just consider that if NDEBUG is not defined -- that is the debug build then! easy!
(0039533)
Francis ANDRE (reporter)
2015-10-08 08:19

 CMake is supposed to help developpers in porting their software on multiple platforms as various as Windows, Linux, OpenVMS and so on...

As stated by Nils Gladitz "_DEBUG is used in the context of Microsoft (and compatible) compilers where it indicates that a debug runtime is being used". Thus code developped on primarely on Windows using _DEBUG cannot be ported as if using CMake while it is the objective of CMake.


"just consider that if NDEBUG is not defined" is not an option because the library imported is a third party and cannot be modified.

By the way, how do you distinguish between 'debugging available and enabled' and 'debugging available but disabled' and 'debugging not available?

How do you manage release build with assert()?
(0039534)
Nils Gladitz (developer)
2015-10-08 09:04

 CMake helps creating portable builds but portability of the source code being build is not within its scope.

Your specific project may rely on _DEBUG being defined but there may also be projects out there which rely on it not being defined.

Users which have written portable source code which does not rely on compiler specific macros like _DEBUG might very much resent CMake for setting it in environments where it is not standard.

Still it is easy enough to define the macro for your own project if that helps with your specific use case without making it a default for everyone else.
(0039535)
Francis ANDRE (reporter)
2015-10-08 09:47

 OK.. so can you do something to avoid such syntax

set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -D_DEBUG")
set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -D_DEBUG")

someting like

CMAKE_C_FLAGS_DEBUG += -D_DEBUG
(0039536)
Nils Gladitz (developer)
2015-10-08 09:56

 The soon to be released CMake 3.4 adds string(APPEND) but until then no.
If you feel up to it you could give it a try with the current release candidate though.

 Issue History
Date Modified Username Field Change
2015-10-08 06:06 Francis ANDRE New Issue
2015-10-08 06:25 Nils Gladitz Note Added: 0039531
2015-10-08 06:28 Alex Turbov Note Added: 0039532
2015-10-08 08:19 Francis ANDRE Note Added: 0039533
2015-10-08 09:04 Nils Gladitz Note Added: 0039534
2015-10-08 09:47 Francis ANDRE Note Added: 0039535
2015-10-08 09:56 Nils Gladitz Note Added: 0039536
2015-10-08 10:52 Brad King Status new => resolved
2015-10-08 10:52 Brad King Resolution open => no change required
2015-10-08 11:14 Francis ANDRE Status resolved => closed

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