Compile multiple C source fles into a unique object file

This is not a usual way to proceed, but you can easily achieve what you want by creating a new final.c file with the following content.

#include "src1.c"
#include "src2.c"
#include "src3.c"

Then you can compile it as follows.

gcc -c final.c -o final.o

Note that there may be issues, read compilation errors, even if each file compiles successfully when compiled separately. This tend to happen especially with macro definitions and includes, when merging your source files into a single one this way.

May be you're looking for this :

ld -r src1.o src2.o src3.o -o final.o

But its always nice to have them archived, using

ar rvs libmy.a file1.o file2.o file3.o

Then use -lmy to link.

To combine multiple source files into a single object file (at least since gcc 4.1), use the compiler/linker option --combine

(edit) later replaced with the compiler option -flto, with linking automatic depending on the compilation state: Requirements to use flto

You can always pipe the files to GCC:

join file1.c file2.c file3.c | gcc -x c -c -o single.o -

Don't forget the option specifying the language, "-x c", which now cannot be deduced from the file extension. You tell GCC to accept input from stdin with the single trailing dash "-".

Note that this is equivalent to compiling a file "final.c" with following contents:

#include "file1.c"
#include "file2.c"
#include "file3.c"

With

gcc -c -o single.o final.c

Just want to say. This is a missing feature.

Why?

say cc can be clang or gcc

cc -c t1.c t2.c (multi-files at once)

vs

cc -c t1.c 
cc -c t2.c
...
(one by one)

What is the difference?

The output .o is same, though the one by one way can specify -o name which may useful when you use cc in your customized toolchain.

The difference is performance. Besides the time for starting up cc, if multi files use same set of .h header files(In most case they will). The header files can load once instead of per file.

Header files could be huge if you use several libraries. A typical .pch (pre-compiled-header) file can as large as 10MB.

In real life test on my small project. I combined all .cpp into one .cpp using #include "others.cpp" , the compile time reduced from 600 ms to 300 ms.

The c/cpp compiles slow, so this could be so useful to be a feature.

could like

cc -c t1.c -o t1.o  t2.c -o t2.o (specify output name per file)

or

cc -c t1.c  t2.c -o mylib.a (If some one say .o can't be combined
   , then link to a lib in one command line)

I hope clang or gcc develop can see this. But not bothering to wait for a fix even they could agreed this opinion.(argue among open source developers can be very hopeless, unless they realize something from self). You can try the method mentioned in other answers like

#include "file1.c"
#include "file2.c"
#include "file3.c"

try using

gcc -o final file1.c file2.c file3.c

it works for me.

Either you make a final.c which will include all .c files then you can compile this final using gcc -c final.c command.

or

Another method is to use archive.Build all files to get respective .o then archive then in one library which will have all those .o file.