Seen this post:
How do you compile a C++ program with multiple class files from OS X Terminal?
I see that to compile with gcc a project with a class (with .h and .cpp) is easy as:
g++ [list of all source files] -o [executableName]
And it actually works for me, but when i try to use Clang:
clang++-11 main.cpp Person.hpp Person.cpp -o main
I get:
clang: error: cannot specify -o when generating multiple output files
NOTE: i know how to use Makefile's, but i would like to have a quick way to compile in Clang like in gcc.
If you run clang++-11 main.cpp Person.hpp Person.cpp -o main with the header file, clang notices this and compiles the pre-compiled header "Person.pch", the default -o Person.pch is implied. Meanwhile you want getting yet another output file "main". Thus, clang complains it can't generate multiple output files, -o Person.pch and -o main.
Pre-compiled headers should be compiled separately.
clang++-11 Person.hpp
clang++-11 main.cpp Person.cpp -o main
The first step is not required, if skipped, no pre-compiled headers are used.
Related
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.
I am trying to make my own header file which will contain a class Vector.
To create a header file, as advised by some websites, I have created two different files :-
1) collections.h (contains declarations)
2) collections.cpp (contains definition)
Another file is main.cpp, which contains the main function, and in which I will be using collections.h
All these files are in the same directory
The trouble I am having is that compiler is showing the error
Undefined reference to Vector::Vector(int, int)
and so on for all the functions in my class.
I have made sure that there is a #include "collections.h" line in both collections.cpp as well as main.cpp
How can I solve the above problem?
I am using gcc compiler under ubuntu 12.04
First build the object files:
gcc -c main.cpp -o main.o
gcc -c collections.cpp -o collections.o
then link them together:
gcc collections.o main.o -o main
You need to build both source files and link them together.
On a Linux command line, you can do it simplest by providing both source files to gcc:
$ g++ -Wall main.cpp collections.cpp -o my_program
Note: I added the -Wall option to enable more warnings by default. It's always a very good habit to enable more warnings, as they can often point out logical errors or possible places where you have undefined behavior.
Recently I have tried to compile a program in g++ (on Ubuntu). Usually i use Dev-C++ (on Windows) and it works fine there as long as I make a project and put all the necessary files in there.
The error that occurs when compiling the program is:
$filename.cpp: undefined reference to '[Class]::[Class Member Function]'
The files used are as following:
The source code (.cpp) file with the main function.
The header file with the function prototypes.
The .cpp file with the definitions for each function.
Any help will be appreciated.
You probably tried to either compile and link instead of just compiling source files or somehow forgot something.
Variation one (everything in one line; recompiles everything all the time):
g++ -o myexecutable first.cpp second.cpp third.cpp [other dependencies, e.g. -Lboost, -LGL, -LSDL, etc.]
Variation two (step by step; if no -o is provided, gcc will reuse the input file name and just change the extension when not linking; this variation is best used for makefiles; allows you to skip unchanged parts):
g++ -c first.cpp
g++ -c second.cpp
g++ -c third.cpp
g++ -o myexecutable first.o second.o third.o [other dependencies]
Variation three (some placeholders):
Won't list it but the parameters mentioned above might as well take placeholders, e.g. g++ -c *.cpp will compile all cpp files in current directory to o(bject) files of the same name.
Overall you shouldn't worry too much about it unless you really have to work without any IDE. If you're not that proficient with the command line syntax, stick to IDEs first.
The command line of gcc should look like:
g++ -o myprogram class1.cpp class2.cpp class3.cpp main.cpp
Check in which cpp file the missing class member function is defined. You may have not given it to gcc.
You can also check for correct #include tags within filename.cpp. Assume that filename.cpp uses code contained in myclass.h present in the same directory as filename.cpp. Assume that the class that g++ says is undefined is contained in myclass.h and defined in myclass.cpp. So, to correctly include myclass.h within filename.cpp, do the following:
In filename.cpp:
#include <iostream>
#include <myclass.h>
//..source code.
In the makefile:
filename.o: myclass.C myclass.h filename.cpp
g++ -I./ -c filename.cpp -o filename.o
myclass.o: myclass.C myclass.h
g++ -c myclass.C -o myclass.o
In the above, note the use of -I. option when compiling filename.cpp. The -I<directory> asks g++ to include the path following the -I part into the search path. That way myclass.h is correctly included.
In the absence of more information (the source maybe), it is difficult to say with any accuracy where the problem lies. All attempts will be but stabs in the dark.
I assume that you have declared a member function (usually in a .h or .hpp file) but have ommited the respective definition of the member function (usually in a .cpp file).
In c++, it is possible to declare a class like so:
class foo {
void x();
void y();
}
with a cpp file that goes like so
void foo::x() {
do_something()
}
Note, there is no foo::y().
This poses no problem to the compiling/linking process as long as the member function foo::y() is referenced nowhere throughout the compiled code.
I've got three files, add.h, add.cpp and test.cpp
add.h creates a header for a class, and is nothing but skeletons for implementation later.
add.cpp contains the actual code for the class listed in add.h
test.cpp contains the main method and declares an instance of the class in add and uses some of its methods.
However, I'm having trouble compiling it. In add.h, I have #DEFINES to prevent multiple writes of the header, and in add.cpp and test.cpp I have add.h included, but when I attempt to compile using the line
g++ test.cpp -o test
I get an error about undefined references to the class objects and methods in add.h. I've been searching google on how to compile or run this, but so far no help, can StackOverflow help me?
EDIT: Sorry, I should have also included that I did try g++ test.cpp add.cpp -o test and it didn't work either, yielding the same resulting errors.
Compile each file separately, then link:
g++ -Wall -c test.cpp
g++ -Wall -c add.cpp
g++ -o test test.o add.o
Or compile and link all files in one command:
g++ -Wall -o test test.cpp add.cpp
run g++ test.cpp add.cpp -o test
EDIT: copypasted my comment here
You need to understand why your initial approach isn't working. When you reference stuff from add.h header in test.cpp, the compiler looks for definitions, but does not find them, because they are in add.cpp and you did not pass it to the compiler. The compiler can't just guess that it should look for the definitions in the add.cpp file just because you included add.h in test.cpp.
run g++ test.cpp add.cpp -o test
or
g++ -c add.cpp -o add.o
g++ -c test.cpp -o test.o
g++ test.o add.o -o test
the -c flag tells gcc to just compile and not link
the first two steps compile 1 cpp (a compilation unit) in an object file
the last step links those into a single executable
your actual problem comes from the fact that when you compile test.cpp, it refers to some simbols which are undefined.
If you're just compiling (-c flag) that's fine, and the next step is to link with those objects file containing the missing symbols.
You need
g++ test.cpp app.cpp -o myTest
as app.cpp contains code used by test.cpp.
I am very aware of compiling C++ programs with g++ in linux environment. But, may be I am missing something, I am getting this strange output/behaviour.
I have source file in test.cpp.
To compile this, I did
(1)
g++ -c test.cpp
g++ -o test test.o
./test
Everything works fine.
But when I did compling and linking in same stage, like this
(2)
g++ test.cpp -o test
./test => Works fine
(3)
g++ -c test.cpp -o test => Doesn't work
In my last case, test is generated but is no more executable; but in my guess it should work fine.
So, what is wrong or do I need to change some settings/configuration ??
I am using g++ 4.3.3
Thanks.
When you say:
g++ -c test.cpp -o test
The -c flag inhibits linking, so no executable is produced - you are renaming the .o file.
Basically, don't do that.
You are forcing compiler to produce an object file and name it like an executable.
Essentially your last line tells: compile this to an object file, but name it test, instead of test.obj.
-c flag means Compile Only
Try
g++ -o test test.cpp
Specifying -o in the g++ command line tells the compiler what name to give the output file. When you tried to do it all in one line, you just told the compiler to compile test.cpp as an object file named test, and no linking was done.
Have a look at the fabulous online manual for GCC for more details.
from the gcc manual:
-c Compile or assemble the source files, but do not link. The linking
stage simply is not done. The ultimate output is in the form of an
object file for each source file.
You must link the compiled object files to get the executable file.
More info about compiling and linking and stuff is here.
Read man g++. The switch -c is to compile only but not to link.
g++ -c test.cpp -o test
does what
g++ -c test.cpp
does but the object file will be test istead of the default name test.o. An object file cannot be executed.