Where does gcc look for C and C header files

Question

On a Unix system  where does gcc look for header files   I spent a little time this morning looking for some system header files  so I thought this would be good information to have here

User · Answer

The set of paths where the compiler looks for the header files can be checked by the command:-

cpp -v

If you declare #include "" , the compiler first searches in current directory of source file and if not found, continues to search in the above retrieved directories.

If you declare #include <> , the compiler searches directly in those directories obtained from the above command.

Source:- http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art026

User · Answer

To get GCC to print out the complete set of directories where it will look for system headers  invoke it like this     LC ALL C gcc -v -E -xc -  lt   dev null 2 gt  amp 1      LC ALL C sed -ne   starts here   End of p    which will produce output of the form   include       search starts here   include  lt     gt  search starts here    usr lib gcc x86 64-linux-gnu 5 include   usr local include   usr lib gcc x86 64-linux-gnu 5 include-fixed   usr include x86 64-linux-gnu   usr include End of search list    If you have -I-family options on the command line they will affect what is printed out    The sed command is to get rid of all the other junk this invocation prints  and the LC ALL C is to ensure that the sed command works -- the  starts here  and  End of search list  phrases are translated IIRC

User · Answer

gcc -print-prog-name cc1plus  -v   This command asks gcc which C   preprocessor it is using  and then asks that preprocessor where it looks for includes   You will get a reliable answer for your specific setup   Likewise  for the C preprocessor    gcc -print-prog-name cpp  -v

User · Answer

You can create a file that attempts to include a bogus system header  If you run gcc in verbose mode on such a source  it will list all the system include locations as it looks for the bogus header     echo   include  lt bogus h gt    gt  t c  gcc -v t c  rm t c         include       search starts here   include  lt     gt  search starts here    usr local include   usr lib gcc i686-apple-darwin9 4 0 1 include   usr include   System Library Frameworks  framework directory    Library Frameworks  framework directory  End of search list         t c 1 32  error  bogus h  No such file or directory

User · Answer

In addition  gcc will look in the directories specified after the -I option

User · Answer

You can create a file that attempts to include a bogus system header  If you run gcc in verbose mode on such a source  it will list all the system include locations as it looks for the bogus header     echo   include  lt bogus h gt    gt  t c  gcc -v t c  rm t c         include       search starts here   include  lt     gt  search starts here    usr local include   usr lib gcc i686-apple-darwin9 4 0 1 include   usr include   System Library Frameworks  framework directory    Library Frameworks  framework directory  End of search list         t c 1 32  error  bogus h  No such file or directory

User · Answer

These are the directories that gcc looks in by default for the specified header files   given that the header files are included in chevrons  lt     1   usr local include  --used for 3rd party header files  2   usr include  -- used for system header files   If in case you decide to put your custom header file in a place other than the above mentioned directories  you can include them as follows  1  using quotes     custom header files foo h   with files path  instead of chevrons in the include statement  2  using the -I switch when compiling the code   gcc -I  home user custom headers  -c foo c -p foo o Basically the -I switch tells the compiler to first look in the directory specified with the -I switch   before it checks the standard directories  When using the -I switch the header files may be included using chevrons

User · Answer

gcc -print-prog-name cc1plus  -v   This command asks gcc which C   preprocessor it is using  and then asks that preprocessor where it looks for includes   You will get a reliable answer for your specific setup   Likewise  for the C preprocessor    gcc -print-prog-name cpp  -v

User · Answer

gcc -print-prog-name cc1plus  -v   This command asks gcc which C   preprocessor it is using  and then asks that preprocessor where it looks for includes   You will get a reliable answer for your specific setup   Likewise  for the C preprocessor    gcc -print-prog-name cpp  -v

User · Answer

The CPP Section of the GCC Manual indicates that header files may be located in the following directories           GCC looks in several different places for headers  On a normal Unix system  if you do not instruct it otherwise  it will look for headers requested with  include  in         usr local include  libdir gcc target version include   usr target include   usr include           For C   programs  it will also look in  usr include g  -v3  first

User · Answer

You can create a file that attempts to include a bogus system header  If you run gcc in verbose mode on such a source  it will list all the system include locations as it looks for the bogus header     echo   include  lt bogus h gt    gt  t c  gcc -v t c  rm t c         include       search starts here   include  lt     gt  search starts here    usr local include   usr lib gcc i686-apple-darwin9 4 0 1 include   usr include   System Library Frameworks  framework directory    Library Frameworks  framework directory  End of search list         t c 1 32  error  bogus h  No such file or directory

User · Answer

In addition  gcc will look in the directories specified after the -I option

User · Answer

g   -print-search-dirs gcc -print-search-dirs

User · Answer

The CPP Section of the GCC Manual indicates that header files may be located in the following directories           GCC looks in several different places for headers  On a normal Unix system  if you do not instruct it otherwise  it will look for headers requested with  include  in         usr local include  libdir gcc target version include   usr target include   usr include           For C   programs  it will also look in  usr include g  -v3  first

User · Answer

The set of paths where the compiler looks for the header files can be checked by the command:-

cpp -v

If you declare #include "" , the compiler first searches in current directory of source file and if not found, continues to search in the above retrieved directories.

If you declare #include <> , the compiler searches directly in those directories obtained from the above command.

Source:- http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art026

User · Answer

You can create a file that attempts to include a bogus system header  If you run gcc in verbose mode on such a source  it will list all the system include locations as it looks for the bogus header     echo   include  lt bogus h gt    gt  t c  gcc -v t c  rm t c         include       search starts here   include  lt     gt  search starts here    usr local include   usr lib gcc i686-apple-darwin9 4 0 1 include   usr include   System Library Frameworks  framework directory    Library Frameworks  framework directory  End of search list         t c 1 32  error  bogus h  No such file or directory

User · Answer

These are the directories that gcc looks in by default for the specified header files   given that the header files are included in chevrons  lt     1   usr local include  --used for 3rd party header files  2   usr include  -- used for system header files   If in case you decide to put your custom header file in a place other than the above mentioned directories  you can include them as follows  1  using quotes     custom header files foo h   with files path  instead of chevrons in the include statement  2  using the -I switch when compiling the code   gcc -I  home user custom headers  -c foo c -p foo o Basically the -I switch tells the compiler to first look in the directory specified with the -I switch   before it checks the standard directories  When using the -I switch the header files may be included using chevrons

User · Answer

To get GCC to print out the complete set of directories where it will look for system headers  invoke it like this     LC ALL C gcc -v -E -xc -  lt   dev null 2 gt  amp 1      LC ALL C sed -ne   starts here   End of p    which will produce output of the form   include       search starts here   include  lt     gt  search starts here    usr lib gcc x86 64-linux-gnu 5 include   usr local include   usr lib gcc x86 64-linux-gnu 5 include-fixed   usr include x86 64-linux-gnu   usr include End of search list    If you have -I-family options on the command line they will affect what is printed out    The sed command is to get rid of all the other junk this invocation prints  and the LC ALL C is to ensure that the sed command works -- the  starts here  and  End of search list  phrases are translated IIRC

User · Answer

In addition  gcc will look in the directories specified after the -I option

User · Answer

g   -print-search-dirs gcc -print-search-dirs

User · Answer

The CPP Section of the GCC Manual indicates that header files may be located in the following directories           GCC looks in several different places for headers  On a normal Unix system  if you do not instruct it otherwise  it will look for headers requested with  include  in         usr local include  libdir gcc target version include   usr target include   usr include           For C   programs  it will also look in  usr include g  -v3  first

User · Answer

The CPP Section of the GCC Manual indicates that header files may be located in the following directories           GCC looks in several different places for headers  On a normal Unix system  if you do not instruct it otherwise  it will look for headers requested with  include  in         usr local include  libdir gcc target version include   usr target include   usr include           For C   programs  it will also look in  usr include g  -v3  first

User · Answer

In addition  gcc will look in the directories specified after the -I option

User · Answer

One could view the  additional  include path for a C program from bash by checking out the following     echo  C INCLUDE PATH   If this is empty  it could be modified to add default include locations  by     export C INCLUDE PATH  C INCLUDE PATH  usr include

User · Answer

gcc -print-prog-name cc1plus  -v   This command asks gcc which C   preprocessor it is using  and then asks that preprocessor where it looks for includes   You will get a reliable answer for your specific setup   Likewise  for the C preprocessor    gcc -print-prog-name cpp  -v

User · Answer

One could view the  additional  include path for a C program from bash by checking out the following     echo  C INCLUDE PATH   If this is empty  it could be modified to add default include locations  by     export C INCLUDE PATH  C INCLUDE PATH  usr include

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