While following the book C++ For Dummies, I have three files in my CodeBlocks project, main.cpp, Pen.h, and Pen.cpp. They look like this:
main.cpp:
#include <iostream>
#include "Pen.h"
//#include "Pen.cpp"
using namespace std;
int main()
{
Pen MyPen = Pen();
MyPen.test();
}
Pen.h:
#ifndef PEN_H_INCLUDED
#define PEN_H_INCLUDED
//#include "Pen.cpp" // Uncommenting this gives a different error
using namespace std;
class Pen
{
public:
// attributes omitted
// PROTOTYPES:
// other functions omitted
void test();
};
#endif // PEN_H_INCLUDED
Pen.cpp:
#include <iostream>
#include "Pen.h"
using namespace std;
//other function definitions omitted
void Pen::test()
{
cout << "Test successful." << endl;
}
When I run the code as listed above, I get an "undefined reference to `Pen::test()'" error. To fix this, I changed the #include statements at the top of main.cpp to:
#include <iostream>
//#include "Pen.h"
#include "Pen.cpp"
This works as intended and correctly prints out "Test successful."
My question is this: what in the world is the point of putting a function prototype in a header file if I have to import the .cpp file later on anyways?
EDIT: It turns out this was a problem with not knowing how to use Code::Blocks rather than with the C++ language.
Assuming you're using gcc, you can compile and link in one step by supplying multiple .cpp files via the command line.
g++ Pen.cpp main.cpp
clang should be similar.
clang++ Pen.cpp main.cpp
An #include should never reference a .cpp file. At all. There's no good reason to do it. Include your headers and then supply the names of all .cpp files when you compile. If your project gets big and you have too many .cpp files to reasonably list, then it's time to break out a makefile or similar.
In the main.cpp include the header file:
#include "Pen.h"
The Pen.h file it's ok.
You need to add the Pen.cpp file to the project tree.
Go to Project -> Add files... and add Pen.cpp
I am practicing using multiple files for C++ in Code::Blocks. I have three files, two source files named main.cpp and Cat.cpp, and a header file named Cat.h. Though I declare a function designed to output text in Cat.h, the implementation in the main function returns the error "'speak' was not declared in this scope."
I tried researching the error, but that was tricky because it's such a general error that can occur for a wide variety of reasons. I tried carefully checking for syntax errors or improper #include statements in my code, but I can't find anything.
This is in my main.cpp file:
#include <iostream>
#include "Cat.cpp"
#include "Cat.h"
using namespace std;
int main()
{
speak();
return 0;
}
this is my Cat.h file:
#ifndef CAT_H_INCLUDED
#define CAT_H_INCLUDED
void speak();
#endif
and this is my Cat.cpp file:
#include <iostream>
#include "Cat.h"
using namespace std;
void speak(){
cout << "Meow!!" << endl;
}
I am expecting speak() to run, but the error says it is not declared in this scope.
I have 21 files as shown here in the picture:
The following 35 functions are declared in lines 364-411 of util.h inside a
#ifndef FlagUtil
#define FlagUtil
#endif
code block:
Create_Pix, Remove_Pix, my_round, edit_error, check_file, check_dir,
read_config, write_config, write_envi_config, my_randomize, my_random,
my_eps_random, cadd, csub, cmul, cdiv, cpwr, cconj, cimg, crel, cmod, cmod2,
angle, cplx_sinc, PolTypeConfig, init_file_name, memory_alloc, PrintfLine,
CreateUsageHelpDataFormat, CreateUsageHelpDataFormatInput,
init_matrix_block, block_alloc, CheckFreeMemory, CheckFreeMemoryWin32,
CheckFreeMemoryLinux
The following 30 functions are declared in lines 99-135 of util_block.h inside a
#ifndef FlagUtilBlock
#define FlagUtilBlock
#endif
code block:
read_matrix_int, read_matrix_float, read_matrix_cmplx, write_matrix_int,
write_matrix_float, write_matrix_cmplx, read_matrix3d_float,
read_matrix3d_cmplx, write_matrix3d_float, write_matrix3d_cmplx,
read_block_matrix_int, read_block_matrix_float,
read_block_matrix_matrix3d_float, read_block_matrix_cmplx,
write_block_matrix_int, write_block_matrix_float,
write_block_matrix_matrix3d_float, write_block_matrix_cmplx,
write_block_matrix3d_float, write_block_matrix3d_cmplx, read_block_S2_avg,
read_block_S2_noavg, read_block_S2T6_avg, read_block_SPP_avg,
read_block_SPP_noavg, read_block_TCI_avg, read_block_TCI_noavg,
read_block_S2_TCIelt_noavg, read_block_SPP_TCIelt_noavg, average_TCI
The following 35 functions are declared in lines 106-149 of util_convert.h inside a
#ifndef FlagUtilConvert
#define FlagUtilConvert
#endif
code block:
S2_to_C3elt, S2_to_C4elt, S2_to_T3elt, S2_to_T4elt, S2_to_T6elt,
SPP_to_C2elt, SPP_to_T2elt, S2_to_SPP, S2_to_IPP, S2_to_C2, S2_to_C3,
S2_to_C4, S2_to_T2, S2_to_T3, S2_to_T4, S2_to_T6, SPP_to_C2, SPP_to_T2,
SPP_to_IPP, SPP_to_T4, C2_to_IPP, C2_to_T2, T2_to_C2, C4_to_T4, C4_to_C3,
C4_to_T3, C4_to_C2, C4_to_IPP, T4_to_C4, T4_to_C3, T4_to_T3, C3_to_T3,
C3_to_C2, C3_to_IPP, T3_to_C3, T6_to_C3
And the contents of the file PolSARproLib.h is:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#ifdef _WIN32
#include <dos.h>
#include <conio.h>
#endif
/* ROUTINES DECLARATION */
#include "util.h"
#include "util_block.h"
#include "util_convert.h"
#include "graphics.h"
#include "matrix.h"
#include "processing.h"
#include "statistics.h"
#include "sub_aperture.h"
#include "my_utils.h"
And the contents of the file PolSARproLib.c is:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <time.h>
#ifdef _WIN32
#include <dos.h>
#include <conio.h>
#endif
/* ROUTINES DECLARATION */
#include "util.c"
#include "util_block.c"
#include "util_convert.c"
#include "graphics.c"
#include "matrix.c"
#include "processing.c"
#include "statistics.c"
#include "sub_aperture.c"
#include "my_utils.c"
I’ve placed those 21 files in a folder named Static Project and I’ve created the PolSARproLib.lib file as follows, my machine is a Win 10x64 one: (here I’ve uploaded this project):
The files graphics.obj, matrix.obj, my_utils.obj, PolSARproLib.lib, PolSARproLib.obj, processing.obj, statistics.obj, sub_aperture.obj, util.obj, util_block.obj, util_convert.obj are created in the Debug folder of the project without any error, but some warnings like:
1>graphics.obj : warning LNK4006: _write_header_bmp_8bit already defined in
PolSARproLib.obj; second definition ignored
I have created a folder named Arii and placed the following 22 files in the subfolder \Arii\lib
I have also the file arii_anned_3components_decomposition.c placed in the folder Arii:
Now I create the project arii_anned_3components_decomposition in the folder Arii as follows (here I’ve uploaded the project)
In the following 2 pictures, you see the configuration of the project. Again, I should say that I’m working on a Win 10x64 machine
External library is added to the project as follows:
Properties>C/C++>General>Additional Include directories
I enter the path to the folder in which header files .h are placed
Properties>Linker>General>Additional library directories
I enter the path to the folder in which .lib files are placed
In
Properties>Linker>Input>Additional Dependencies
I’ve entered name of those needed .lib files:
Here is the beginning (before main function) of the file arii_anned_3components_decomposition.c:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include "omp.h"
#ifdef _WIN32
#include <dos.h>
#include <conio.h>
#endif
/* ROUTINES DECLARATION */
#include "../lib/PolSARproLib.h"
Now I build the solution:
And unfortunately I get 104 errors. 100 of them is about multiple definition of the functions in util.h, util_convert.h, util_block.h (those functions are listed in the beginning of question)
Errors 1-100 are alike:
1>PolSARproLib.lib(PolSARproLib.obj) : error LNK2005: _C3_to_T3 already
defined in PolSARproLib.lib(util_convert.obj)
Here I’ve uploaded the error and warning file.txt
I really don’t understand why am I getting these errors regarding that the code blocks #ifndef #define #endif have been used in the
code?
As stated by CoryKramer, we don't need the file PolSARpro.c, in fact we should never #include .cpp or .c files and this is what has been done in that file:
The contents of the file PolSARproLib.c is:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <time.h>
#ifdef _WIN32
#include <dos.h>
#include <conio.h>
#endif
/* ROUTINES DECLARATION */
#include "util.c"
#include "util_block.c"
#include "util_convert.c"
#include "graphics.c"
#include "matrix.c"
#include "processing.c"
#include "statistics.c"
#include "sub_aperture.c"
#include "my_utils.c"
So, in order to get rid of all those 100 LNK2005 errors, simply place these 20 files (Omit PolSARproLib.c) in a folder
And do the next steps as stated in the question for creating and building the static library project PolSARproLib.lib file and for creating and building the console application project arii_anned_3components_decomposition.exe file.
I have created simple win32 console application:
#include "stdafx.h"
#include <iostream>
#include "conio.h"
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
cout << "Hello World" << endl;
int num;
cin >> num;
return 0;
}
It compiles fine.
Then I'm trying to add library. I Have dll lib and .h files.
I have included my.h file:
#include "stdafx.h"
#include "my.h"
#include <iostream>
#include "conio.h"
"my.h" contains lines:
#ifndef __AFXWIN_H__
#error include 'stdafx.h' before including this file for PCH
#endif
After compile I got error:
include 'stdafx.h' before including this file for PCH
But I have already included 'stdafx.h'. I have tested with both options of Use/Not use precompile headers - the same result. Where is the problem?
Your my.h is using MFC (__AFXWIN_H__ is defined by MFC headers) but your console program is not. You must use MFC in your program or rewrite your library to not use MFC.
Do not include external headers or stdafx.h in your headers.
Include all external headers in stdafx.h.
Include stdafx.h from every cpp file in your project.
This will build faster too as the external headers are processed once via PCH.
here is the structure of my program:
// File: main.cpp
#include <iostream>
#include <math.h>
using namespace std;
#include "do.cpp"
int main()
{
doit();
}
// File: do.cpp
void doit()
{
cout<<sqrt(2)<<endl;
}
When I do
g++ main.cpp
Everything goes fine. Now, if I open this as an Xcode project (I have chosen "Command line utility" as project type) and try to just build and run, it keeps saying:
Use of undeclared identifier sqrt
Unknown type name 'ostream'
What should I be supposed to do? Did I do something wrong?
Thank you very much!
Matteo
Don't do this:
#include "do.cpp"
but instead put that "do.cpp" file in the same Xcode project, alongside your main.m or main.cpp file.
And when you want to build from the command line, you can do:
g++ main.cpp do.cpp -o mytesttool
which would create the command line tool named "mytesttool".
The explanation is quite simple actually. You probably added both files to the project. Xcode tries to compile each file into an object file and then link them together.
When it tries to compile do.cpp it doesn't find the definition of cout because iostream is not included and neither math.h for sqrt, as part of do.cpp.
That file compiles fine when compiled as part of main.cpp, because it is included in the file and it finds iostream and math.h and also the using declaration.
Anyway if you remove do.cpp from the project (just the reference) everything should compile as expected.
The right way without a header file
// File: main.cpp
void doit(); // declare the function
int main()
{
doit();
}
// File: do.cpp
#include <iostream>
#include <math.h>
using namespace std;
void doit()
{
cout<<sqrt(2)<<endl;
}
The right way with a header file
// File do.h
#ifndef __DO_H_
#define __DO_H_
void doit();
#endif // __DO_H_
// File: main.cpp
#include "do.h"
int main()
{
doit();
}
// File: do.cpp
#include <iostream>
#include <math.h>
#include "do.h"
using namespace std;
void doit()
{
cout<<sqrt(2)<<endl;
}
When making the new file, I forgot to de-check the "target" selection, so that when it tried to build the project it tried to build all the single files and then link them together. By disabling the "target", I got it to work.