Can gcc output C code after preprocessing

Question

I m using an open source library which seems to have lots of preprocessing directives to support many languages other than C  So that I can study what the library is doing I d like to see the C code that I m compiling after preprocessing  more like what I d write   Can gcc  or any other tool commonly available in Linux  read this library but output C code that has the preprocessing converted to whatever and is also readable by a human

User · Answer

cpp is the preprocessor    Run cpp filename c to output the preprocessed code  or better  redirect it to a file with cpp filename c  gt  filename preprocessed

User · Answer

Run   gcc -E  lt file gt  c   or  g   -E  lt file gt  cpp

User · Answer

Suppose we have a file as Message cpp or a  c file  Steps 1  Preprocessing  Argument -E    g   -E   Message cpp   P1  P1 file generated has expanded macros and header file contents and comments are stripped off   Step 2  Translate Preprocessed file to assembly  Argument -S   This task is done by compiler  g   -S   Message cpp  An assembler  ASM  is generated  Message s   It has all the assembly code   Step 3  Translate assembly code to Object code  Note  Message s was generated in Step2  g   -c   Message s  An Object file with the name Message o is generated  It is the binary form   Step 4  Linking the object file  This task is done by linker  g     Message o -o MessageApp  An exe file MessageApp exe is generated here    include  lt iostream gt  using namespace std      This a sample program   int main     cout  lt  lt   Hello   lt  lt  endl   cout  lt  lt  PQR P K    getchar    return 0

User · Answer

Yes  Pass gcc the -E option  This will output preprocessed source code

User · Answer

-save-temps This is another good option to have in mind  gcc -save-temps -c -o main o main c  main c  define INC 1  int myfunc int i        return i   INC     and now  besides the normal output main o  the current working directory also contains the following files   main i is the desired prepossessed file containing    1  quot main c quot    1  quot  lt built-in gt  quot    1  quot  lt command-line gt  quot    31  quot  lt command-line gt  quot    1  quot  usr include stdc-predef h quot  1 3 4   32  quot  lt command-line gt  quot  2   1  quot main c quot    int myfunc int i        return i   1      main s is a bonus  -  and contains the generated assembly       file    quot main c quot       text      globl  myfunc      type   myfunc   function myfunc   LFB0       cfi startproc     pushq    rbp      cfi def cfa offset 16      cfi offset 6  -16     movq     rsp   rbp      cfi def cfa register 6     movl     edi  -4  rbp      movl    -4  rbp    eax     addl     1   eax     popq     rbp      cfi def cfa 7  8     ret      cfi endproc  LFE0       size   myfunc   -myfunc      ident   quot GCC   Ubuntu 8 3 0-6ubuntu1  8 3 0 quot       section     note GNU-stack  quot  quot   progbits    If you want to do it for a large number of files  consider using instead   -save-temps obj  which saves the intermediate files to the same directory as the -o object output instead of the current working directory  thus avoiding potential basename conflicts  The advantage of this option over -E is that it is easy to add it to any build script  without interfering much in the build itself  Another cool thing about this option is if you add -v  gcc -save-temps -c -o main o -v main c  it actually shows the explicit files being used instead of ugly temporaries under  tmp  so it is easy to know exactly what is going on  which includes the preprocessing   compilation   assembly steps   usr lib gcc x86 64-linux-gnu 8 cc1 -E -quiet -v -imultiarch x86 64-linux-gnu main c -mtune generic -march x86-64 -fpch-preprocess -fstack-protector-strong -Wformat -Wformat-security -o main i  usr lib gcc x86 64-linux-gnu 8 cc1 -fpreprocessed main i -quiet -dumpbase main c -mtune generic -march x86-64 -auxbase-strip main o -version -fstack-protector-strong -Wformat -Wformat-security -o main s as -v --64 -o main o main s  Tested in Ubuntu 19 04 amd64  GCC 8 3 0  CMake predefined targets CMake automatically provides a targets for the preprocessed file  make help  shows us that we can do  make main i  and that target runs  Preprocessing C source to CMakeFiles main dir main c i  usr bin cc    -E  home ciro bak hello main c  gt  CMakeFiles main dir main c i  so the file can be seen at CMakeFiles main dir main c i Tested on cmake 3 16 1

User · Answer

I m using gcc as a preprocessor  for html files   It does just what you want  It expands   --  directives  then outputs a readable file   NONE of the other C HTML preprocessors I ve tried do this- they concatenate lines  choke on special characters  etc    Asuming you have gcc installed  the command line is   gcc -E -x c -P -C -traditional-cpp code before cpp     code after cpp   Doesn t have to be  cpp    There s an excellent description of this usage at http   www cs tut fi  jkorpela html cpre html   The  -traditional-cpp  preserves whitespace  amp  tabs

[c] Can gcc output C code after preprocessing?

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