I use g++ 10.2.0 and try to create a static library, but when I create object file for archiving a static library, object file format always shows precompiled header, it makes the final static library cannot work:
//file static_test.cpp
void fn(){
int temp;
++temp;
}
//file static_test.h
void fn();
build them but not link
g++ -c static_test.h static_test.cpp -o static_test.o
use file to show static_test.o format
file static_test.o
static_test.o:GCC precompiled header (version 014) for C++
and I archive it
ar rsv libstatic_test.a static_test.o
use file to show libstatic_test.a format:
current ar archive
use a main.cpp to test this static library
#include "static_test.h"
int main(){
fn();
return 0;
}
compile them and link
g++ main.cpp libstatic_test.a
libstatic_test.a: cannot add symbol: archive has no index；run ranlib to add one
collect2: error：ld return 1
why and how to solve this problem, tks~
-c is only for a single file, the second static_test.cpp is ignored. You should get the compiler warning about multiple files set to -c. g++ -c static_test.h results the precompiled header in static_test.o and static_test.cpp is ignored. The proper command should be
g++ -c static_test.cpp -o static_test.o
Do not pass header files to the compiler when you compile object files. All other commands you are using look ok.
if you would like to create a static library with gcc, you have to say it to the linker/wrapper programm "gcc" like:
gcc -static -o libyourlibname(.lib/.so) obj1.o obj2.o -s
legende:
-static: tells the linker to build a static lib
-o : output file
-s : strip all debug/linking stuff, including debug informations
note:
may be you need the option -fPIC at .c compile time like:
gcc -O2 -fPIC -c file1.c -o file1.o
legende:
-O2 : tells the c compiler to optimize
-fPIC : create program independet code (internal for the output code)
-c : compile C file to object file:
-o : tell the linker how the object file should be named
By the way:
Pre-compiled header files are only created by compiling C/C++ files only.
You have require huge memory, and mostly pre-compiled header files are not needed in small projects of small student homework tasks.
And each time you change the header file, you (the compiler) have to create a new copy of the .pch file.
Of course, .pch files are good for end-products which does not change it in the form for the developer. But they are mostly depend on the compiler.
So, you can't use .pch files from Windows MinGW64 Project under Linux (with the near) same compiler in different versions.
Related
I'm having a custom C header file that I have created. There are several files in my directory as follows.
lib1/
-lib1.h
-lib1.c
lib2/
-lib2.h
-lib2.c
-lib_main.c
-lib_main.h
-main.c
-main.cpp
-Makefile
Now, for testing the header file with a test file called main.c, I will be giving the following command in the terminal,
gcc lib_main.c lib1/lib1.c lib2/lib2.c main.c -o ./main
Now, how could I test the same header files with main.cpp instead of main.c, how do I change it?
You should (and most probably must) compile separately the c and c++ sources into a object file, and then link together.
As an example
gcc -c -o lib1.o lib1/lib1.c
gcc -c -o lib2.o lib2/lib1.c
gcc -c -o lib_main.o lib_main.c
g++ -c -o main.o main.cpp
g++ -o main lib1.o lib2.o lib_main.o main.o
The first four commands create a series of object files, with extension .o. The last command link together the object files into an executable.
Obviously you need to add the relevant compiler options for each source.
Two important points to notice:
Order of files in the linking is important. See discussion here and here.
To mix c and c++ code with each other, for example if a c++ code calls a c function, you need to follow specific guidelines.
I want to use OpenGL GLEW library. I have the binary downloaded and its folder is in the folder with my .cpp file. My .cpp file uses #include <eglew.h>.
How should I format my command for MinGW to compile my .cpp file? Do I compile with the .lib file like g++ -L./path/to/lib/file.lib test.cpp -o test or do I do something else like link to the header files g++ -I./path/to/headers test.cpp -o test?
To better understand things maybe it's better to split compiling and linking steps.
If you get errors then you will also know in which step the problem occurs.
I'm assuming you have the following folders/files:
/path/to/eglew/include/GL/eglew.h
/path/to/eglew/lib/libglew32.a
Compiling:
g++ -Wall -c -o test.o test.cpp -I/path/to/eglew/include/GL
Linking:
g++ -o test.exe test.o -L/path/to/eglew/lib -lglew32
Though I would expect to see #include <GL/eglew.h> in which case the linker include flag should be -I/path/to/eglew/include.
For example, I'm given carModels.cpp, carModels.h, carType.in, manufacturers.h, manufacturers.o, and lastly my own file tester.cpp. How would I go about linking all of these using g++ in a Linux terminal? Would I have to create any additional ".o" files? I'm supposed to assume that the given files already work. Multiple lines in terminal are fine, I just I want a clear understanding of it. (I'm coming from a C++ IDE that I didn't really care for.)
Compile each source file to its own object file:
g++ -I . -c carModels.cpp -o carModels.o
g++ -I . -c tester.cpp -o tester.o
Now link all object files together:
g++ carModels.o tester.o manufacturers.o -o outputname
Consider adding more options like -O3, -std=c++11, -Wall, etc. as needed.
you can do this in two steps, first compile to *.o files,
gcc -c your.cpp other.cpp .....
then link them
gcc -o you_out_put_name the_object_files.o ...
In a single line, that would be just g++ -o tester *.cpp *.o. GCC will sort everything out. In particular, the *.h files are referenced via #include "" statements in the .cpp files.
Ok, so this might not be a great question, but I'm a bit stuck.
I have 3 programs:
pegio.c/pegio.h - Does hardware initialization and functions for my device
PegIOHandler.cpp/PegIOHandler.h - Handles I/O for device
PegRTU.cpp - Main function
My project implements the opendnp3 (which allows one to transmit data using the DNP3 protocol) library.
Now, to compile it I first compile the pegio.c file
gcc -c pegio.c -o pegio.o
Easy, up to here I understand.
Secondly I compile the IOHandler and reference pegio.c as it uses it.
g++ -c PegIOHandler.cpp pegio.c -o PegIOHandler.o -std=c++0x
Now it gives me the following output.
g++: warning: pegio.o: linker input file unused because linking not done
But, it still creates the object file. HOWEVER, PegIOHandler implements opendnp3 header files, which is included in PegIOHandler.cpp and PegIOHandler.h. When I attempt to compile these files without using the '-c', it tells me that there are undefined references to the opendnp3 files. I know I have to link them to my project, but how do I do that?
Then compililing my third and final file:
g++ PegRTU.cpp pegio.o PegIOHandler.o -o pegrtu -std=c++0x
This now tells me that there are undefined references to the opendnp3 files.
So: How do I link the opendnp3 library to my project / code files???
Thanks!
Ouch. So many misunderstandings. You don't need the previously compiled object files to compile further source files to object code. However, you do need to link them together at the end of the compilation process, including any libraries required. All in all:
gcc -c pegio.c -o pegio.o
g++ -c PegIOHandler.cpp -o PegIOHandler.o -std=c++0x
g++ -c PegRTU.cpp -o PegRTU.o -std=c++0x
g++ -o executable_name *.o -lopendnp3 # or whatever linker flag is needed for OpenDNP3
And pretty please, read this.
Recently I had to use this command in a makefile I had for an sqlite program I'm working on:
gcc -g -c sqlite3.c -o sqlite3.o
g++ -g -c main.cpp -o main.o
g++ sqlite3.o main.o -o sqliteex
I had to directly compile the sqlite3.c file into my program in order to use the sqlite3.h interface (included in the main.cpp file with #include SQL/sqlite3.h). But why did I need to use gcc to do this and create sqlite3.o, then compile both files as .o files into my executable?
Edit: My guess would be that .o files are compilable by both gcc and g++, if this is the case, is it a good practice to just always compile things as .o files?
But why did I need to use gcc to do this and create sqlite3.o, then compile both files as .o files into my executable?
You did not need to do that. The reason you did do that was to specify that sqlite.c was C code and not C++ code. You could have done this instead:
g++ main.cpp -x c sqlite3.c -o sqliteex
Additionally, it is possible (but not at all certain) that the sqlite code could have compiled as C++, like this:
g++ main.cpp sqlite3.c -o sqliteex
Quote from Wikipedia:
Single Compilation Unit is a technique of computer programming for the C/C++ languages, which reduces compilation time and aids the compiler to perform program optimization even when the compiler itself is lacking support for whole program optimization or precompiled headers.
http://en.wikipedia.org/wiki/Single_Compilation_Unit
Development is mostly edit->compile until success cycle. When you have separately compiled files you can just recompile only file which was modified, which makes rebuild much faster. Last line is not compilation but linking of compiled object files into target executable.
Also as Mysticial noted, you have mixture of C and C++