I want to make my project available for Linux.
Therefore, I need to substitute functions from windows.h library.
In my terminal.cpp I highlight error messages in red. This step I only want to do in windows OS (ANSI don't work for my console, so i don't have a cross-platform solution for this).
On windows it works, but on Linux i get the following error:
/usr/bin/ld: /tmp/ccvTgiE8.o: in function `SetConsoleTextAttribute(int, int)':
Terminal.cpp:(.text+0x0): multiple definition of `SetConsoleTextAttribute(int, int)'; /tmp/cclUawx7.o:main.cpp:(.text+0x0): first defined here
collect2: error: ld returned 1 exit status
In my main.cpp file I do nothing but include terminal.h and run it.
terminal.cpp
if (OS_Windows)
{
SetConsoleTextAttribute(dependency.hConsole, 4);
cout << "Error: " << e.getMessage() << endl;
SetConsoleTextAttribute(dependency.hConsole, 7);
}
else
{
cout << "Error: " << e.getMessage() << endl;
}
terminal.h
#ifdef _WIN32
#define OS_Windows 1
#include "WindowsDependency.h"
#else
#define OS_Windows 0
#include "UnixDependency.h"
#endif
WindowsDependency.h
#pragma once
#include <Windows.h>
class Dependency
{
public:
HANDLE hConsole = GetStdHandle(STD_OUTPUT_HANDLE);
};
UnixDependency.h
#pragma once
class Dependency
{
public:
int hConsole = 0;
};
void SetConsoleTextAttribute(int hConsole, int second) {};
Header files are supposed to contain declarations. By adding the {} you made a definition and C++ does not allow multiple definitions of the same function with identical signatures.
Either remove the {} and provide a definition in a separately-compiled .cpp file, OR by marking the function as inline.
Related
I encountered this problem when I try to compile my code
I thought it might be caused by header files including each other. But as far as I can tell I did not find any issues with my header files
Error LNK1169 one or more multiply defined symbols
found Homework2 D:\05Development\04 C_C++\C\DS Alg
class\Homework2\Debug\Homework2.exe 1
also, there's an error telling me that function Assert() has been declared elsewhere.
Error LNK2005 "void __cdecl Assert(bool,class
std::basic_string,class
std::allocator >)"
(?Assert##YAX_NV?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std###Z)
already defined in DataBase.obj Homework2 D:\05Development\04
C_C++\C\DS Alg class\Homework2\Homework2\dbTest.obj 1
here's the structure of my code:
function
void Assert(bool val, string s)
{
if (!val)
{
cout << "Assertion Failed!!: " << s << endl;
exit(-1);
}
}
is in Constants.h
A virtual class List includes Constants.h
#pragma once // List.h
#include "Constants.h"
An array list includes List class, in the AList class it calls the Assert function
#pragma once //AList.h
#include "List.h"
...
Assert((pos >= 0) && (pos < listSize), "Position out of range");
In the DataBase class I created a AList member
private:
AList<CData> set;
header looks like this:
#pragma once
#include "AList.h"
#include "CData.h"
and CData.h looks like this:
#pragma once
class CData
{
private:
std::string m_name;
int m_x;
int m_y;
public:
CData(std::string str = "null", int x = 0, int y = 0) : m_name(str), m_x(x), m_y(y) {}
// Helper functions
const std::string& GetName() const { return this->m_name; }
const int& GetX() const { return this->m_x; }
const int& GetY() const { return this->m_y; }
};
When you build your project, each .cpp file gets compiled separately into different object files. The once in #pragma once only applies to the compilation of a single .cpp file, not for the project as a whole. Thus if a .cpp file includes header A and header B, and header B also includes header A, then the second include of header A will be skipped.
However, if you have another .cpp file that includes A, A will be included in that object file again -- because #pragma once only works when compiling a single .cpp file.
An #include statement literally takes the content of the included file and "pastes" it into the file that included it. You can try this by looking at the output of the C preprocessor tool (cpp in the gcc toolchain). If you are using the gcc toolchain, you can try something like this to see the file after its includes have been applied:
cpp file.cpp -o file_with_includes.cpp
If you have a function in your header, like Assert in your example, the function gets replicated into each .cpp file you include it in.
If you have A.cpp and B.cpp, that both include your Constants.h file, each object file (.o or .obj depending on your environment) will include a copy of your Assert function. When the linker combines the object files to create a binary, both object files will declare that they provide the definition for Assert, and the linker will complain, because it doesn't know which one to use.
The solution here is either to inline your Assert function, like this:
inline void Assert(bool val, string s)
{
if (!val)
{
cout << "Assertion Failed!!: " << s << endl;
exit(-1);
}
}
or to provide its body in its own .cpp file, leaving only the function prototype in the header.
Constants.h:
void Assert(bool val, string s);
Constants.cpp:
void Assert(bool val, string s)
{
if (!val)
{
cout << "Assertion Failed!!: " << s << endl;
exit(-1);
}
}
Mind you, the Standard Library also offers assert(), which works nicely too. (see https://en.cppreference.com/w/cpp/error/assert).
#include <cassert>
...
assert(is_my_condition_true());
assert(my_variable > 23);
// etc..
Just keep in mind that the assert declared in cassert only works when compiling for Debug, and gets compiled out when building for Release (to speed up execution), so don't put any code in assert that has side effects.
#include <cassert>
...
// Don't call functions with side effects.
// Thus function decreases a "count" and returns the new value
// In Release builds, this line will disappear and the decrement
// won't occur.
assert(myclass.decrement_count() > 0);
I'm new to codelite and c++. I'm using Linux and the g++ compiler. I've set up a simple project with two source files just to play around with linker errors. The files look like so:
Main.cpp:
#include <iostream>
void Log(const char*);
static int Multiply (int a, int b)
{
Log("Multiply");
return a * b;
}
int main()
{
std::cout << Multiply(5, 8) << std::endl;
std::cin.get();
}
Log.cpp:
#include <iostream>
void Log(const char* message)
{
std::cout << message << std::endl;
}
As you can see, Log.cpp simply specifies a function called in main. Both files are in the same directory, "src". So far all my settings are pretty much default, still I get an "undefined reference to `Log(..." error when I try to build this project.
Also, if I comment out the declaration of the Log function at the top of main.cpp, I would expect a compilation error since an undeclared function being called. Yet if I try to compile main.cpp I get no errors.
This is what my workspace looks like
Project settings
Compiler settings
Linker settings
Am I correct to expect the behaviors described above? Is there some setting I have to manually configure?
I am trying to export a function pointer for a function to be called. What I am after is when a function in a dll/exe needs to call a function exported by another library it gets the function pointer and calls that. The reason for this is I want to provide a hooking mechanism and I figured function pointers would be the quickest and easiest way because I can change what they point to easily are runtime.
So I found this Exporting a function pointer from dll and I cant get it to work. Whenever I call it to get the function pointer I get an error that it cant find the entry point. So the error isnt that the function pointer is working but the function to get the function pointer isnt working. I believe it is a function signature issue. Here is an example:
Colors.h
#ifndef __COLORS
#define __COLORS
#ifdef MYDLL_EXPORTS
/*Enabled as "export" while compiling the dll project*/
#define DLLEXPORT __declspec(dllexport)
#else
/*Enabled as "import" in the Client side for using already created dll file*/
#define DLLEXPORT __declspec(dllimport)
#endif
#include <string>
#include <vector>
class Colors
{
private:
std::string myColor;
static DLLEXPORT std::vector<std::string> allColors;
public:
Colors(){};
Colors(std::string MyColor);
virtual DLLEXPORT std::string getMyColor();
virtual DLLEXPORT void addToColors(std::string color);
std::vector<std::string> getAllColors();
};
typedef Colors* (*create)(std::string);
DLLEXPORT create createColors();
Colors* createColors2(std::string color);
#endif
colors.cpp
#define MYDLL_EXPORTS
#include "Color.h"
std::vector<std::string> Colors::allColors;
Colors::Colors(std::string MyColor)
{
this->myColor = MyColor;
this->allColors.push_back(this->myColor);
}
std::vector<std::string> Colors::getAllColors()
{
return this->allColors;
}
std::string Colors::getMyColor()
{
return this->myColor;
}
Colors* createColors2(std::string color)
{
return new Colors(color);
}
DLLEXPORT void Colors::addToColors(std::string color)
{
this->allColors.push_back(color);
}
DLLEXPORT create createColors()
{
return &createColors2;
}
main.cpp
#define MYDLL_EXPORTS
#include <iostream>
#include <Windows.h>
#include "Color.h"
int main()
{
Colors red("red");
Colors blue("blue");
Colors* dlltest;
//Define the function prototype
typedef Colors* (*createNewColor)();
BOOL freeResult, runTimeLinkSuccess = FALSE;
HINSTANCE dllHandle = NULL;
createNewColor dllCreateNewColor = NULL;
//Load the dll and keep the handle to it
dllHandle = LoadLibrary(L"libs/testerdll.dll");
// If the handle is valid, try to get the function address.
if (NULL != dllHandle)
{
//Get pointer to our function using GetProcAddress:
dllCreateNewColor = (createNewColor)GetProcAddress(dllHandle,"createNewColor");
// If the function address is valid, call the function.
if (runTimeLinkSuccess = (NULL != dllCreateNewColor))
{
dlltest = dllCreateNewColor();
std::cout << "Color of dll class: " << dlltest->getMyColor() << std::endl;
}
else
{
std::cout << "Failed to locate function" << std::endl;
}
//Free the library:
//freeResult = FreeLibrary(dllHandle);
}
else
{
std::cout << "Failed to load library" << std::endl;
}
std::vector<std::string> colorslist = red.getAllColors();
for (std::string color : colorslist)
{
std::cout << color << std::endl;
}
return 0;
}
Dll project
dllmain.cpp
// testerdll.cpp : Defines the exported functions for the DLL application.
#include "stdafx.h"
#include "Color.h"
__declspec(dllexport) Colors* createNewColor()
{
create temp1 = createColors(); //seems to fail here
return nullptr;
}
Yes I know I have memory leaks etc. this was just a quick example code to replicate the problem.
To return the function, you need to get it's address, and return that
e.g.
__declspec(dllexport) create createNewColor()
{
create temp1 = createColors;
return temp1;
}
However, this system (using std::string as a return type, requires that both the .exe and the .dll use the same DLL based runtime library.
stackoverflow : passing reference to STL over function boundary
C++ does not define a calling convention between files. This means that different compilers may set up C++ objects slightly differently. Microsoft limited that with the definition of COM, but that still is a possibility.
Also for visual studio, there are separate heaps (new / delete) between runtime instances. When you link against the dynamic library, all dlls and exes in the process share this DLL. But then they all need to be updated together.
So this process can work, but be wary about :-
Sharing C++ types between binaries (DLL/EXE) - no ABI
Using new in DLL, and delete in EXE. (different heaps).
STL objects are also problematic, as they are a mixture of header implementation (compiled into the binary), and DLL implementation (compiled into C++ runtime).
Is it possible to call routines from an external file like notepad (or also cpp file if needed)?
e.g.
I have 3 files.
MainCode.cpp
SubCode_A.cpp <- not included in the headers of the MainCode.cpp
SubCode_B.cpp <- not included in the headers of the MainCode.cpp
MainCode_A.cpp
#include <iostream>
using namespace std;
int main ()
{
int choice = 0;
cin >> choice;
if (choice == 1)
{
"call routines from SubCode_A.cpp;" <- is there a possible code for this?
}
else if (choice == 2)
{
"call routines from SubCode_B.cpp;" <- is there a possible code for this?
}
return 0;
}
=================================
SubCode_A.cpp CODES
{
if (1) //i need to include if statement :)
cout >> "Hello World!!";
}
=================================
SubCode_B.cpp CODES
{
if (1) //i need to include if statement :)
cout >> "World Hello!!";
}
Make the code in e.g. SubCode_A.cpp a function, then declare this function in your main source file and call it. You of course have to build with all source files to create the final executable.
You can just use an #include statement.
Include instructs the compiler to insert the specified file at the #include point.
So your code would be
if (choice == 1)
{
#include "SubCode_A.cpp"
}
...
And you wouldn't need the extra braces in the SubCode_?.cpp files because they exist in MainCode.cpp
Of course, the compiler will only compile what is in the SubCode files at the time of compilation. Any changes to source that aren't compiled won't end up in your executable.
But mid source #includes doesn't lend itself to very readable code.
No
You have to compile both codes,
Declare an external function (e.g. extern void function (int);, in a header.
Compile those two files which will include this header.
Then in a 3rd file, where you use it just include the header.
BUT as you include all the 3 files in the compilation it will work.
This other post maybe useful : Effects of the extern keyword on C functions
It is not possible to call the code in another executable. It is possible for one application to expose an "api" (application programming interface) through a library or DLL which allows you to call some of the code that the application uses.
While compiling YOUR code, though, the compiler needs to know the "fingerprint" of the functions you are going to call: that is, what it returns and what arguments it takes.
This is done through a declaration or "prototype stub":
// subcode.h
void subCodeFunction1(); // prototype stub
void subCodeFunction3(int i, int j);
// subcode.cpp
#include <iostream>
void subCodeFunction1()
{
std::cout << "subCodeFunction1" << std::endl;
}
void subCodeFunction2()
{
std::cout << "subCodeFunction2" << std::endl;
}
void subCodeFunction3(int i, int j)
{
std::cout << "subCodeFunction1(" << i << "," << j << ")" << std::endl;
}
// main.cpp
#include "subcode.h"
int main() {
subCodeFunction1(); // ok
subCodeFunction2(); // error: not in subcode.h, comment out or add to subcode.h
subCodeFunction3(2, 5); // ok
return 0;
}
I tried compiling a simple program on Xcode and got the following messages:
function<anonymous namespace>::Initialize' has internal linkage but is not defined
function<anonymous namespace>::HandleBadInput' has internal linkage but is not defined
Undefined symbols for architecture x86_64:
"(anonymous namespace)::Initialize()", referenced from:
_main in main.o
"(anonymous namespace)::HandleBadInput()", referenced from:
_main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
The header file looks like this:
#ifndef WJKErrorHandling
#define WJKErrorHandling
namespace WJKErrorHandling{
void Initialize(void);
int HandleBadInput(void);
}
#endif // defined(WJKErrorHandling)
the implementation file looks like this:
#include <iostream>
#include "WJKErrorHandling.h"
namespace WJKErrorHandling{
void Initialize(void){
std::cin.exceptions(std::cin.failbit);
}
int HandleBadInput(void){
std::cerr << "Input Error: wrong type?\n";
std::cin.clear();
char BadInput[5];
std::cin >> BadInput;
return 1;
}
}
and main.cpp looks like this:
#include <iostream>
#include "WJKErrorHandling.h"
void Prompt (void){
//Prompts the user to begin entering numbers
std::cout << "Begin entering numbers: \n";
}
float GetNumber (void){
std::cout << "Number: \n";
float Number;
std::cin >> Number;
return Number;
}
std::string GetString (void){
std::cout << "String: \n";
std::string String;
std::cin >> String;
return String;
}
int main()
{
Prompt();
WJKErrorHandling::Initialize();
int ReturnCode = 0;
try{
float Number = GetNumber();
std::cout << Number;
std::string String = GetString();
std::cout << String;
std::cout << "SUCCESS!!!!\n";
}
catch(...){
ReturnCode = WJKErrorHandling::HandleBadInput();
}
return ReturnCode;
}
I've tried finding an answer so far, but I haven't understood any of the posts that I've found. I'm new with C++, so any help would be greatly appreciated!
Your #define Guard is causing name lookup issue.
change to below style should fix the issue:
#ifndef WJK_ERROR_HANDLING_H
#define WJK_ERROR_HANDLING_H
You could also use the non-standard but more idiomatic #pragma once, according to its wikipedia page it is supported by all major compilers.
Since many compilers have optimizations to identify include guards, there is no speed advantage between the two. For myself I see the following advantages of #pragma once:
It has only one meaning (whereas defines serve different purposes) and will not clash with other things (e.g. a namespace as in your case).
It is little to type and simple to remember.
You cannot have errors due to a typo (WJKERRORHANDLNG_H, ups and I is missing), because you started the header as a copy of another and forgot to change the include guard, which gives you rather nasty bughunting sessions.
This turns out to be a bad include guard:
#ifndef WJKErrorHandling
#define WJKErrorHandling
because you later try to use WJKErrorHandling as a namespace, but the macro makes it go away.
Change your include guard to something like:
#ifndef WJKERRORHANDLING_H
#define WJKERRORHANDLING_H
which is probably more idiomatic and less likely to conflict with something.