I can't figure out why i can't compile my program with
g++ -std=c++0x main.cpp Sale.h iProduct.h -o w7
every time i try and compile with this command i get a clang error
clang: error: cannot specify -o when generating multiple output files
the program complies fine as a.out and i know i could just rename the a.out file and be on my way but i would like to know why I'm getting this error and how i should fix it.
Thanks
why I'm getting this error and how i should fix it
may I ask why do the .h files affect it?
Because of recent versions of gcc can compile heaader files,
Example:
g++ test.h -o out
file out
out: GCC precompiled header (version 014) for C++
It(gcc) produce precompiled files (https://en.wikipedia.org/wiki/Precompiled_header) in this case.
So when you compile .cpp file and header at the same time,
it can not decide what produce as output precompiled headers, or elf executable.
Related
I've just inherited some C++ code that was written poorly with one cpp file which contained the main and a bunch of other functions. There are also .h files that contain classes and their function definitions.
Until now the program was compiled using the command g++ main.cpp. Now that I've separated the classes to .h and .cpp files do I need to use a makefile or can I still use the g++ main.cpp command?
list all the other cpp files after main.cpp.
ie
g++ main.cpp other.cpp etc.cpp
and so on.
Or you can compile them all individually. You then link all the resulting ".o" files together.
To compile separately without linking you need to add -c option:
g++ -c myclass.cpp
g++ -c main.cpp
g++ myclass.o main.o
./a.out
Now that I've separated the classes to .h and .cpp files do I need to use a makefile or can I still use the "g++ main.cpp" command?
Compiling several files at once is a poor choice if you are going to put that into the Makefile.
Normally in a Makefile (for GNU/Make), it should suffice to write that:
# "all" is the name of the default target, running "make" without params would use it
all: executable1
# for C++, replace CC (c compiler) with CXX (c++ compiler) which is used as default linker
CC=$(CXX)
# tell which files should be used, .cpp -> .o make would do automatically
executable1: file1.o file2.o
That way make would be properly recompiling only what needs to be recompiled. One can also add few tweaks to generate the header file dependencies - so that make would also properly rebuild what's need to be rebuilt due to the header file changes.
.h files will nothing to do with compiling ... you only care about cpp files... so type g++ filename1.cpp filename2.cpp main.cpp -o myprogram
means you are compiling each cpp files and then linked them together into myprgram.
then run your program ./myprogram
I know this question has been asked years ago but still wanted to share how I usually compile multiple c++ files.
Let's say you have 5 cpp files, all you have to do is use the * instead of typing each cpp files name E.g g++ -c *.cpp -o myprogram.
This will generate "myprogram"
run the program ./myprogram
that's all!!
The reason I'm using * is that what if you have 30 cpp files would you type all of them? or just use the * sign and save time :)
p.s Use this method only if you don't care about makefile.
You can still use g++ directly if you want:
g++ f1.cpp f2.cpp main.cpp
where f1.cpp and f2.cpp are the files with the functions in them. For details of how to use make to do the build, see the excellent GNU make documentation.
As rebenvp said I used:
g++ *.cpp -o output
And then do this for output:
./output
But a better solution is to use make file. Read here to know more about make files.
Also make sure that you have added the required .h files in the .cpp files.
You can use several g++ commands and then link, but the easiest is to use a traditional Makefile or some other build system: like Scons (which are often easier to set up than Makefiles).
If you want to use #include <myheader.hpp> inside your cpp files you can use:
g++ *.cpp -I. -o out
I used to use a custom Makefile that compiled all the files in current directory, but I had to copy it in every directory I needed it, everytime.
So I created my own tool - Universal Compiler which made the process much easier when compile many files.
You can do that using a single command assuming all the needed .cpp and .h files are in the same folder.
g++ *.cpp *.h -Wall && ./a.out
It will compile and execute at the same time.
when using compiler in the command line, you should take of the following:
you need not compile a header file, since header file gets substituted in the script where include directive is used.
you will require to compile and link the implementation and the script file.
for example let cow.h be header file and cow.cpp be implementation file and cow.cc(c++ files can have extension .cpp, .cc, .cxx, .C, .CPP, .cp) be script file.
Since gcc compiler notation for c++ file is g++, we can compile and link the files using
$g++ -g -Wall cow.cpp cow.cc -o cow.out
options '-g' and '-Wall' are for debugging info and getting warning for errors. Here cow.out is the name of the executable binary file that we can execute to run the program. it is always good to name your executable file otherwise name will be automatically given which might be confusing at times.
you can also do the same by using makefiles, makefiles will detect, compile and link automatically the specified files.
There are great resources for compilation using command line
enter link description here
~/In_ProjectDirectory $ g++ coordin_main.cpp coordin_func.cpp coordin.h
~/In_ProjectDirectory $ ./a.out
... Worked!!
Using Linux Mint with Geany IDE
When I saved each file to the same directory, one file was not saved correctly within the directory; the coordin.h file. So, rechecked and it was saved there as coordin.h, and not incorrectly as -> coordin.h.gch. The little stuff.
Arg!!
I am working on a database project that compiles queries (expressed in some higher level language) into c++ code. This code is compiled and executed by the database. That part works perfectly fine.
Right now, I am trying to reduce the compile time for the C++ query code. I was wondering whether I can use precompiled headers to gain performance here.
The query is translated into a file called Query.cpp which includes library/src/Database.hpp. The Database.hpp file includes further files like StandardTypes.hpp and so on. Can I precompile all those header files to speed up the compilation of Query.cpp? If yes, how can I do that? I could not find any good example for precompiled headers so far, only some really basic stuff.
I use the following command to compile Query.cpp:
clang++ -fPIC -std=c++11 Query.cpp -I./library/src/ -shared -o libquery.so;
to create pre-compiled header include all the headers you don't change into Query.h and use:
clang -cc1 Query.h -emit-pch -o Query.h.pch
to use the pre-compiled header type:
clang -cc1 -include-pch Query.h.pch Query.cpp -shared -o libquery.so;
Query.cpp needs to include Query.h
Im a beginner in C++ and working with unix. So here is my question.
I`ve written few lines in the main-function, and i needed a function, that is defined in the c_lib - library.
main.cpp:
#include <iostream>
#include "c_lib.cpp"
int main()
{
return 0;
}
i want to execute it on the terminal, so i wrote
g++ -c c_lib.cpp
g++ -c main.cpp
g++ -o run c_lib.o main.o
Until here, there is no error report.
Then
./run
I get the error
error: ./run: No such file or directory
What's wrong?
Including a .cpp is not usually done, usually only headers are included. Headers usually contain the declarations that define the interface to the code in the other .cpp
Can you show us the source of c_lib? That may help.
As the source of c_lib is #included, there is no need to compile it seperately. In fact this can/will cause errors (multiple definitions being the first to come to mind). You should only need to do:
g++ -o run main.cpp
to compile your code in this case.
(When using a header (.h), you will need to compile the implementation (.cpp) seperately)
Compile with warnings turned on:
g++ -Wall -Wextra -o run main.cpp
and you will get more output if there are problems with your code.
Is the run file being output by gcc? You can test by calling ls in the terminal (or ls run to only show the executable if it is present).
If the executable is present, it could be that it isn't marked as runnable. I'll go into that if it is a problem as it is outside the general scope of the site (though still related)
First of all you should not include source file into another source. You should create a header file and put declarations there (that allows main() to call functions from c_lib.cpp or use global variables if any)
When you run g++ you have to look into it's output, if operation succeed or not. In your case it failed so executable run was not created.
Usually you do not call compiler manually but write a makefile and let make utility to call g++.
I'm doing some experiment about extern keywork and currently working on Fedora 19 and g++.
Im trying to compile multiple c++ files and execute the program. Here it compiled successfully. but when try to run it shows Permission denied error. I change to permission using chmod to 777. but still result is same. then I try to compile and run a simple Hello World program and That works fine. Whats wrong with my program?
test1.h
int a=0;
test2.h
#include <iostream>
using namespace std;
extern int a;
void foo()
{
cout << "This is a test string " << endl;
cout << a << endl;
}
int main()
{
foo();
}
Here is how I compiled and the execute result of theTerminal
[root#localhost cpp]# g++ test1.h test2.h -o test.o
[root#localhost cpp]# ./test.o
bash: ./test.o: Permission denied
[root#localhost cpp]#
You have several problems. If you use the file(1) utility to inspect the output file, you'll realize why it can't be executed:
$ file test.o
test.o: GCC precompiled header (version 013) for C++
Precompiled header files are not valid executable files—they're not valid ELF files and they're not script files with a shbang line, they're just data files that the compiler knows how to read.
Why are you getting a precompiled header file? Because you're asking g++ to compile header files (.h files). It's really ridiculous to give your C++ source files .h extensions, because they're not header files, they're source files. Give them the proper .cc or .cpp extensions, and g++ will compile them correctly to an executable.
Secondly, why are you giving the output file the name test.o? .o is used for object files (compiled versions of singular source files, not complete executables), but you're asking g++ to compile a full executable. If you only want to compile and not also link, then pass the -c flag, and then manually link the object files together. Don't name your executables with .o. test would be the more proper name for an executable compiled from a source file named test.cc, but I'd caution against that and recommend using something else, because test is also the name of a shell builtin function.
When you compile .h files using g++, the compiler generates precompiled header files. These are not executable files. They won't run even if you changed their permissions to 777.
Look for This program is also useful when precompiling a C header file with a ‘.h’ extension for use in C++ compilations. at https://gcc.gnu.org/onlinedocs/gcc-4.8.3/gcc/Invoking-G_002b_002b.html#Invoking-G_002b_002b.
Try these commands:
g++ -o test.o test1.h
file test.o
You should get the output
test.o: GCC precompiled header (version 014) for C++
To create an executable, rename the files to test1.cc and test2.cc. Then, build the executable from them using
g++ -o test test1.cc test2.cc
Now, you will be able to execute the program using:
./test
I've just inherited some C++ code that was written poorly with one cpp file which contained the main and a bunch of other functions. There are also .h files that contain classes and their function definitions.
Until now the program was compiled using the command g++ main.cpp. Now that I've separated the classes to .h and .cpp files do I need to use a makefile or can I still use the g++ main.cpp command?
list all the other cpp files after main.cpp.
ie
g++ main.cpp other.cpp etc.cpp
and so on.
Or you can compile them all individually. You then link all the resulting ".o" files together.
To compile separately without linking you need to add -c option:
g++ -c myclass.cpp
g++ -c main.cpp
g++ myclass.o main.o
./a.out
Now that I've separated the classes to .h and .cpp files do I need to use a makefile or can I still use the "g++ main.cpp" command?
Compiling several files at once is a poor choice if you are going to put that into the Makefile.
Normally in a Makefile (for GNU/Make), it should suffice to write that:
# "all" is the name of the default target, running "make" without params would use it
all: executable1
# for C++, replace CC (c compiler) with CXX (c++ compiler) which is used as default linker
CC=$(CXX)
# tell which files should be used, .cpp -> .o make would do automatically
executable1: file1.o file2.o
That way make would be properly recompiling only what needs to be recompiled. One can also add few tweaks to generate the header file dependencies - so that make would also properly rebuild what's need to be rebuilt due to the header file changes.
.h files will nothing to do with compiling ... you only care about cpp files... so type g++ filename1.cpp filename2.cpp main.cpp -o myprogram
means you are compiling each cpp files and then linked them together into myprgram.
then run your program ./myprogram
I know this question has been asked years ago but still wanted to share how I usually compile multiple c++ files.
Let's say you have 5 cpp files, all you have to do is use the * instead of typing each cpp files name E.g g++ -c *.cpp -o myprogram.
This will generate "myprogram"
run the program ./myprogram
that's all!!
The reason I'm using * is that what if you have 30 cpp files would you type all of them? or just use the * sign and save time :)
p.s Use this method only if you don't care about makefile.
You can still use g++ directly if you want:
g++ f1.cpp f2.cpp main.cpp
where f1.cpp and f2.cpp are the files with the functions in them. For details of how to use make to do the build, see the excellent GNU make documentation.
As rebenvp said I used:
g++ *.cpp -o output
And then do this for output:
./output
But a better solution is to use make file. Read here to know more about make files.
Also make sure that you have added the required .h files in the .cpp files.
You can use several g++ commands and then link, but the easiest is to use a traditional Makefile or some other build system: like Scons (which are often easier to set up than Makefiles).
If you want to use #include <myheader.hpp> inside your cpp files you can use:
g++ *.cpp -I. -o out
I used to use a custom Makefile that compiled all the files in current directory, but I had to copy it in every directory I needed it, everytime.
So I created my own tool - Universal Compiler which made the process much easier when compile many files.
You can do that using a single command assuming all the needed .cpp and .h files are in the same folder.
g++ *.cpp *.h -Wall && ./a.out
It will compile and execute at the same time.
when using compiler in the command line, you should take of the following:
you need not compile a header file, since header file gets substituted in the script where include directive is used.
you will require to compile and link the implementation and the script file.
for example let cow.h be header file and cow.cpp be implementation file and cow.cc(c++ files can have extension .cpp, .cc, .cxx, .C, .CPP, .cp) be script file.
Since gcc compiler notation for c++ file is g++, we can compile and link the files using
$g++ -g -Wall cow.cpp cow.cc -o cow.out
options '-g' and '-Wall' are for debugging info and getting warning for errors. Here cow.out is the name of the executable binary file that we can execute to run the program. it is always good to name your executable file otherwise name will be automatically given which might be confusing at times.
you can also do the same by using makefiles, makefiles will detect, compile and link automatically the specified files.
There are great resources for compilation using command line
enter link description here
~/In_ProjectDirectory $ g++ coordin_main.cpp coordin_func.cpp coordin.h
~/In_ProjectDirectory $ ./a.out
... Worked!!
Using Linux Mint with Geany IDE
When I saved each file to the same directory, one file was not saved correctly within the directory; the coordin.h file. So, rechecked and it was saved there as coordin.h, and not incorrectly as -> coordin.h.gch. The little stuff.
Arg!!