FILE macro shows full path

Question

The standard predefined macro   FILE   available in C shows the full path to the file  Is there any way to short the path  I mean instead of   full path to file c   I see  to file c   or   file c

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Here s a solution that works for environments that don t have the string library  Linux kernel  embedded systems  etc     define FILENAME          const char  filename start     FILE          const char  filename   filename start        while  filename      0             filename          while  filename    filename start   amp  amp     filename - 1                     filename--        filename       Now just use FILENAME instead of   FILENAME    Yes  it s still a runtime thing but it works

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Here is the solution that uses compile-time calculation   constexpr auto  getFileName const char  const path        const auto  startPosition   path      for  const auto  currentCharacter   path  currentCharacter      0     currentCharacter                if   currentCharacter             currentCharacter                               startPosition   currentCharacter                       if  startPosition    path                  startPosition             return startPosition     std  cout  lt  lt  getFileName   FILE

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Use the basename   function  or  if you are on Windows   splitpath      include  lt libgen h gt    define PRINTFILE     char buf       FILE    printf  Filename    s n   basename buf        Also try man 3 basename in a shell

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A tweaked  even more  quot bloated quot  version of red1ynx s answer   define   FILENAME        strchr   FILE                  strrchr   FILE            strrchr   FILE            1     FILE             strrchr   FILE           strrchr   FILE           1     FILE       If we find backslashes  we split on backslashes  Otherwise  split on forward slash  Simple enough  Just about any alternative would be cleaner  A C   constexpr is really the gold standard here  in my opinion   However  this may be helpful if you re using some compiler where   BASE FILE   isn t available

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In VC  when using  FC    FILE   expands to the full path  without the  FC option   FILE   expands file name  ref  here

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Recent Clang compiler has a   FILE NAME   macro  see here

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A short  working answer for both Windows and  nix    define   FILENAME   std  max lt const char  gt    FILE         std  max strrchr   FILE          1  strrchr   FILE         1

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Here is a portable function that works for both Linux  path      and Windows  mix of     and         Compiles with gcc  clang and vs    include  lt string h gt   include  lt stdio h gt   const char  GetFileName const char  path        const char  name   NULL   tmp   NULL      if  path  amp  amp   path            name   strrchr path                tmp   strrchr path                 if  tmp                 return name  amp  amp  name  gt  tmp   name   1   tmp   1                      return name   name   1   path     int main         const char  name   NULL   path   NULL       path     FILE        name   GetFileName path       printf  path   s  filename   s n   path  name        path    tmp device log       name   GetFileName path       printf  path   s  filename   s n   path  name        path    C   Downloads  crisis avi       name   GetFileName path       printf  path   s  filename   s n   path  name        path    C   Downloads nda pdf       name   GetFileName path       printf  path   s  filename   s n   path  name        path    C  Downloads  word doc       name   GetFileName path       printf  path   s  filename   s n   path  name        path   NULL      name   GetFileName NULL       printf  path   s  filename   s n   path  name        path           name   GetFileName          printf  path   s  filename   s n   path  name        return 0      Standard output   path  test c  filename  test c path   tmp device log  filename  device log path  C  Downloads crisis avi  filename  crisis avi path  C  Downloads nda pdf  filename  nda pdf path  C  Downloads word doc  filename  word doc path   null   filename   null  path    filename

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If you are using CMAKE with GNU compiler this global define works fine    set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -D  MY FILE        notdir   abspath   lt

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There s no compile time way to do this  Obviously you can do it at runtime using the C runtime  as some of the other answers have demonstrated  but at compile time  when the pre-procesor kicks in  you re out of luck

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A slight variation on what  red1ynx proposed would to be create the following macro    define SET THIS FILE NAME         static const char  const THIS FILE NAME             strrchr   FILE           strrchr   FILE           1     FILE      In each of your  c pp  files add   SET THIS FILE NAME      Then you can refer to THIS FILE NAME instead of   FILE     printf   s n   THIS FILE NAME     This means the construction is performed once per  c pp  file instead of each time the macro is referenced   It is limited to use only from  c pp  files and would be unusable from header files

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At least for gcc  the value of   FILE   is the file path as specified on the compiler s command line  If you compile file c like this   gcc -c  full path to file c   the   FILE   will expand to   full path to file c   If you instead do this   cd  full path to gcc -c file c   then   FILE   will expand to just  file c    This may or may not be practical   The C standard does not require this behavior  All it says about   FILE   is that it expands to  The presumed name of the current source  le  a character string literal     An alternative is to use the  line directive  It overrides the current line number  and optionally the source file name  If you want to override the file name but leave the line number alone  use the   LINE   macro   For example  you can add this near the top of file c    line   LINE    file c    The only problem with this is that it assigns the specified line number to the following line  and the first argument to  line has to be a digit-sequence so you can t do something like   line    LINE  -1   file c      This is invalid   Ensuring that the file name in the  line directive matches the actual name of the file is left as an exercise   At least for gcc  this will also affect the file name reported in diagnostic messages

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If you ended up on this page looking for a way to remove absolute source path that is pointing to ugly build location from the binary that you are shipping  below might suit your needs   Although this doesn t produce exactly the answer that the author has expressed his wish for since it assumes the use of CMake  it gets pretty close  It s a pity this wasn t mentioned earlier by anyone as it would have saved me loads of time   OPTION CMAKE USE RELATIVE PATHS  If true  cmake will use relative paths  ON    Setting above variable to ON will generate build command in the format    cd  ugly absolute path to project build src  amp  amp       gcc  lt    other flags    gt  -c       src path to source c   As a result    FILE   macro will resolve to       src path to source c  CMake documentation  Beware of the warning on the documentation page though      Use relative paths  May not work      It is not guaranteed to work in all cases  but worked in mine - CMake 3 13   gcc 4 5

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Try   include  lt string h gt    define   FILENAME    strrchr   FILE           strrchr   FILE           1     FILE      For Windows use      instead of

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I have use the same solution with  Patrick  s answer for years   It has a small issue when the full path contains symbol-link   Better solution   set CMAKE C FLAGS    CMAKE C FLAGS  -Wno-builtin-macro-redefined -D   FILE       subst   realpath   CMAKE SOURCE DIR       abspath   lt         set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -Wno-builtin-macro-redefined -D   FILE       subst   realpath   CMAKE SOURCE DIR       abspath   lt           Why should use this     -Wno-builtin-macro-redefined to mute the compiler warnings for redefining   FILE   macro      For those compilers do not support this  refer to the Robust way below   Strip the project path from the file path is your real requirement  You won t like to waste the time to find out where is a header h file  src foo header h or src bar header h  We should strip the   FILE   macro in cmake config file   This macro is used in most exists codes  Simply redefine it can set you free   Compilers like gcc predefines this macro from the command line arguments  And the full path is written in makefiles generated by cmake  Hard code in CMAKE   FLAGS is required   There is some commands to add compiler options or definitions in some more recently version  like add definitions   and add compile definitions    These commands will parse the make functions like subst before apply to source files  That is not we want    Robust way for -Wno-builtin-macro-redefined   include CheckCCompilerFlag  check c compiler flag -Wno-builtin-macro-redefined SUPPORT C WNO BUILTIN MACRO REDEFINED  if  SUPPORT C WNO BUILTIN MACRO REDEFINED      set CMAKE C FLAGS    CMAKE C FLAGS  -Wno-builtin-macro-redefined   endif  SUPPORT C WNO BUILTIN MACRO REDEFINED  include CheckCXXCompilerFlag  check cxx compiler flag -Wno-builtin-macro-redefined SUPPORT CXX WNO BUILTIN MACRO REDEFINED  if  SUPPORT CXX WNO BUILTIN MACRO REDEFINED      set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -Wno-builtin-macro-redefined   endif  SUPPORT CXX WNO BUILTIN MACRO REDEFINED       Remember to remove this compiler option from the set   FLAGS     -D  FILE        line

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GCC 8 now has the -fmacro-prefix-map and -ffile-prefix-map options   -fmacro-prefix-map old new When preprocessing files residing in directory old  expand the   FILE   and   BASE FILE   macros as if the files resided in directory new instead  This can be used to change an absolute path to a relative path by using   for new which can result in more reproducible builds that are location independent  This option also affects   builtin FILE   during compilation  See also -ffile-prefix-map    -ffile-prefix-map old new When compiling files residing in directory old  record any references to them in the result of the compilation as if the files resided in directory new instead  Specifying this option is equivalent to specifying all the individual -f -prefix-map options  This can be used to make reproducible builds that are location independent  See also -fmacro-prefix-map and -fdebug-prefix-map   Setting an invalid path for -ffile-prefix-map  -fdebug-prefix-map  will break debugging unless you tell your debugger how to map back   gdb  set substitue-path  vscode   quot sourceFileMap quot    If your intent is to only clean up   FILE   just use -fmacro-prefix-map  Example  So for my Jenkins builds I will add -ffile-prefix-map   WORKSPACE      and another to remove the local dev package install prefix  NOTE Unfortunately the -ffile-prefix-map and -fmacro-prefix-map options are only available in GCC 8 onwards   For  say  GCC 5  we only have -fdebug-prefix-map which does not affect   FILE

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Purely compile time solution here  It s based on the fact that sizeof   of a string literal returns its length 1    define STRIPPATH s        sizeof s   gt  2  amp  amp   s  sizeof s -2            s    sizeof s  - 1         sizeof s   gt  3  amp  amp   s  sizeof s -3            s    sizeof s  - 2         sizeof s   gt  4  amp  amp   s  sizeof s -4            s    sizeof s  - 3         sizeof s   gt  5  amp  amp   s  sizeof s -5            s    sizeof s  - 4         sizeof s   gt  6  amp  amp   s  sizeof s -6            s    sizeof s  - 5         sizeof s   gt  7  amp  amp   s  sizeof s -7            s    sizeof s  - 6         sizeof s   gt  8  amp  amp   s  sizeof s -8            s    sizeof s  - 7         sizeof s   gt  9  amp  amp   s  sizeof s -9            s    sizeof s  - 8         sizeof s   gt  10  amp  amp   s  sizeof s -10            s    sizeof s  - 9         sizeof s   gt  11  amp  amp   s  sizeof s -11            s    sizeof s  - 10    s     define   JUSTFILE   STRIPPATH   FILE      Feel free to extend the conditional operator cascade to the maximum sensible file name in the project  Path length doesn t matter  as long as you check far enough from the end of the string   I ll see if I can get a similar macro with no hard-coded length with macro recursion

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include  lt algorithm gt   include  lt string gt  using namespace std  string f    FILE      f   string   find f rbegin    f rend         1  base     1  f end          searches for the     from the back  transfers the reverse iterator     into a forward iterator and constructs a new sting with both

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C  11 msvc2015u3 gcc5 4 clang3 8 0  template  lt typename T  size t S gt  inline constexpr size t get file name offset const T   amp  str  S   size t i   S - 1        return  str i            str i             i   1    i  gt  0   get file name offset str  i - 1    0      template  lt typename T gt  inline constexpr size t get file name offset T   amp  str  1         return 0         int main          printf   s n    amp   FILE   get file name offset   FILE            Code generates a compile time offset when    gcc  at least gcc6 1   -O1 msvc  put result into constexpr variable     constexpr auto file    amp   FILE   get file name offset   FILE        printf   s n   file    clang  persists on not compile time evaluation   There is a trick to force all 3 compilers does compile time evaluation even in the debug configuration with disabled optimization       namespace utility            template  lt typename T  T v gt          struct const expr value                       static constexpr const T value   v                          define UTILITY CONST EXPR VALUE exp    utility  const expr value lt decltype exp   exp gt   value      int main                  printf   s n    amp   FILE   UTILITY CONST EXPR VALUE get file name offset   FILE                https   godbolt org z u6s8j3

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I have just thought of a great solution to this that works with both source and header files  is very efficient and works on compile time in all platforms without compiler-specific extensions  This solution also preserves the relative directory structure of your project  so you know in which folder the file is in  and only relative to the root of your project   The idea is to get the size of the source directory with your build tool and just add it to the   FILE   macro  removing the directory entirely and only showing the file name starting at your source directory   The following example is implemented using CMake  but there s no reason it wouldn t work with any other build tools  because the trick is very simple   On the CMakeLists txt file  define a macro that has the length of the path to your project on CMake     The additional   is important to remove the last character from the path    Note that it does not matter if the OS uses   or    because we are only   saving the path size  string LENGTH    CMAKE SOURCE DIR    SOURCE PATH SIZE  add definitions  -DSOURCE PATH SIZE   SOURCE PATH SIZE      On your source code  define a   FILENAME   macro that just adds the source path size to the   FILE   macro    define   FILENAME      FILE     SOURCE PATH SIZE    Then just use this new macro instead of the   FILE   macro  This works because the   FILE   path will always start with the path to your CMake source dir  By removing it from the   FILE   string the preprocessor will take care of specifying the correct file name and it will all be relative to the root of your CMake project   If you care about the performance  this is as efficient as using   FILE    because both   FILE   and SOURCE PATH SIZE are known compile time constants  so it can be optimized away by the compiler   The only place where this would fail is if you re using this on generated files and they re on a off-source build folder  Then you ll probably have to create another macro using the CMAKE BUILD DIR variable instead of CMAKE SOURCE DIR

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I did a macro   FILENAME   that avoids cutting full path each time  The issue is to hold the resulting file name in a cpp-local variable    It can be easily done by defining a static global variable in  h file  This definition gives separate and independent variables in each  cpp file that includes the  h  In order to be a multithreading-proof it worth to make the variable s  also thread local  TLS    One variable stores the File Name  shrunk   Another holds the non-cut value that   FILE   gave  The h file   static   declspec  thread   const char  fileAndThreadLocal strFilePath   NULL  static   declspec  thread   const char  fileAndThreadLocal strFileName   NULL    The macro itself calls method with all the logic    define   FILENAME         GetSourceFileName   FILE    fileAndThreadLocal strFilePath  fileAndThreadLocal strFileName    And the function is implemented this way   const char  GetSourceFileName const char  strFilePath                                 const char  amp  rstrFilePathHolder                                 const char  amp  rstrFileNameHolder        if strFilePath    rstrFilePathHolder                               This if works in 2 cases              - when first time called in the cpp  ordinary case  or            - when the macro   FILENAME   is used in both h and cpp files               and so the method is consequentially called                 once with strFilePath     UserPath HeaderFileThatUsesMyMACRO h  and                 once with strFilePath     UserPath CPPFileThatUsesMyMACRO cpp                     rstrFileNameHolder   removePath strFilePath           rstrFilePathHolder   strFilePath            return rstrFileNameHolder      The removePath   can be implemented in different ways  but the fast and simple seems to be with strrchr   const char  removePath const char  path        const char  pDelimeter   strrchr  path             if  pDelimeter          path   pDelimeter 1       pDelimeter   strrchr  path            if  pDelimeter          path   pDelimeter 1       return path

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just hope to improve FILE macro a bit    define FILE  strrchr   FILE           strrchr   FILE           1   strrchr   FILE            strrchr   FILE            1     FILE     this catches   and    like Czarek Tomczak requested  and this works great in my mixed environment

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Since you are using GCC  you can take advantage of       BASE FILE   This macro expands to the name of the main input file  in the form of a C string constant  This is the source file that was   specified on the command line of the preprocessor or C compiler   and then control how you want to display the filename by changing the source file representation  full path relative path basename  at compilation time

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Try   pragma push macro    FILE      define   FILE    foobar c    after the include statements in your source file and add    pragma pop macro    FILE       at the end of your source file

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Here s a tip if you re using cmake   From  http   public kitware com pipermail cmake 2013-January 053117 html  I m copying the tip so it s all on this page   set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -D  FILENAME        subst     CMAKE SOURCE DIR      abspath   lt           If you re using GNU make  I see no reason you couldn t extend this to your own makefiles   For example  you might have a line like this   CXX FLAGS  -D  FILENAME        subst   SOURCE PREFIX      abspath   lt          where   SOURCE PREFIX  is the prefix that you want to remove   Then use   FILENAME   in place of   FILE

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