[CMake] Last minute build-date file.

[David Cole]

On Fri, Oct 15, 2010 at 12:17 PM, Michael Hertling <mhertling at online.de>wrote:

> On 10/15/2010 04:14 PM, william.crocker at analog.com wrote:
> > Hello:
> >
> > If my app requires relinking, then at link time
> > I would like to capture the current date and time and place it
> > in a last-minute source file which is linked with the application.
> > Following is my attempt at this with CMake.
> >
> > The problems I can see are:
> > 1 - It is not portable as it uses the OS date command.
> > 2 - It is not portable as it calls gcc directly.
> > 3 - It will not work with Debug or Release builds unless
> >      I set additional target LINK_FLAGS_<type> properties.
> > 4 - I wish the creation of the link_date.cc file could be
> >      done inline of the add_custom_command instead of requiring
> >      a separate file. (I got into quoting hell.)
> > 5 - Sneaking link_date.o onto the link line with the LINK_FLAGS
> >      property is kind of a hack.
> >
> > Suggestions please.
> >
> > Thanks in advance.
> >
> > Bill
> >
> > -------------------- CMake code --------------
> >
> > # Note that this is a simplified version of the real thing
> > # and may contain syntax errors.
> >
> > add_executable( myapp myapp.cc  )
> > target_link_libraries( myapp lib1 lib2 )
> > set_target_properties( myapp PROPERTIES LINK_FLAGS link_date.o )
> >
> > add_custom_command(
> >      TARGET myapp PRE_LINK
> >      COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/create_link_date
> >      COMMAND gcc -m32 -c -I${UTILDIR} link_date.cc
> >      COMMENT "Make the link_date file"
> >      VERBATIM
> > )
> >
> > ------------- Contents of create_link_date ----------
> >
> > #!/bin/csh
> >
> > echo 'const char *link_date() { return("'`date`'"); }' > link_date.cc
>
> You might use CMake's --build option when hooking into the linking stage:
>
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
> PROJECT(LINKDATE C)
> FILE(WRITE ${CMAKE_BINARY_DIR}/main.c "
> #include <stdio.h>
> int main(void)
> {
>    printf(\"%s\\n\",linkdate());
>    return 0;
> }")
> FILE(WRITE ${CMAKE_BINARY_DIR}/linkdate.c.in "
> const char *linkdate() { return(\"@LINKDATE@\"); }
> ")
> FILE(WRITE ${CMAKE_BINARY_DIR}/linkdate.cmake "
> EXECUTE_PROCESS(
>    COMMAND date
>    OUTPUT_VARIABLE LINKDATE
>    OUTPUT_STRIP_TRAILING_WHITESPACE
> )
> CONFIGURE_FILE(\${SRC} \${DST} @ONLY)
> ")
> ADD_CUSTOM_COMMAND(
>    OUTPUT ${CMAKE_BINARY_DIR}/linkdate.c
>    COMMAND ${CMAKE_COMMAND} -DSRC=linkdate.c.in -DDST=linkdate.c
>                             -P linkdate.cmake
>    DEPENDS ${CMAKE_BINARY_DIR}/linkdate.c.in)
> ADD_LIBRARY(linkdate STATIC EXCLUDE_FROM_ALL linkdate.c)
> ADD_EXECUTABLE(main main.c)
> TARGET_LINK_LIBRARIES(main linkdate)
> ADD_CUSTOM_COMMAND(
>    TARGET main
>    PRE_LINK
>    COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_BINARY_DIR}/linkdate.c.in
>    COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR}
>                             --target linkdate)
>
> This rebuilds the target linkdate - a static library containing the
> desired timestamp - just before the main target is linked against it.
> Thus, the problems you mentioned should be solved except for #1 which
> can not be done in a platform-independent manner at the moment, AFAIK.
>
> Regards,
>
> Michael
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But if you're going to write a C program anyway....

...then just use "time" and/or "gmtime" standard library functions to print
the date/time out in whatever format you want.
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