I have the following class definition and for some reason I cannot define the threadpool inside the class definition itself. It says: syntax error: identifier 'numberofpoolthreads' I tried directly defining it in the class, but it gives me same syntax error, does anyone know why this is?
#include "stdafx.h"
#include <boost/threadpool.hpp>
#include <boost/threadpool/pool.hpp>
#include <boost/threadpool/detail/pool_core.hpp>
typedef boost::threadpool::fifo_pool resolverpool;
class ResolverThreadPoolManager
{
public:
ResolverThreadPoolManager::ResolverThreadPoolManager(int numberofpoolthreads);
ResolverThreadPoolManager::~ResolverThreadPoolManager();
resolverpool p(numberofpoolthreads);
private:
int numberofpoolthreads;
};
This line: resolverpool p(numberofpoolthreads); isn't valid in a class definition. You need a member variable, which you then initialise in the constructor. e.g.:
class ResolverThreadPoolManager
{
public:
explicit ResolverThreadPoolManager(int numberofpoolthreads);
...
private:
const resolverpool p;
};
ResolverThreadPoolManager::ResolverThreadPoolManager(int numberofpoolthreads)
: p(numberofpoolthreads)
{}
In your line
resolverpool p(numberofpoolthreads);
the argument "numberofpoolthreads" is not a type, so this is a malformed declaration. Perhaps
resolverpool p(int numberofpoolthreads);
? I imagine, perhaps incorrectly, that your error message also hints on which line the error occurred, which can help narrow down where in a file an error lies. (Although, typically only indicating "error is on this or some previous line.")
Related
I'm having a hard time figuring out how to solve this C2027 compiler error:
"A type cannot be used until it is defined. To resolve the error, be sure the type is fully defined before referencing it".
This is CPU.h:
// CPU.h
#include "Register.h"
class Register;
class CPU
{
public:
static const enum class Flag { CARRY = 4, HALF_CARRY, SUBTRACT, ZERO };
private:
Register A;
};
And this is Register.h:
// Register.h
#include "CPU.h"
class CPU;
class Register
{
void foo(const CPU::Flag& flag); // error C2027
};
So I now that this error is because CPU class hasn't initialize yet and I'm aware of the option the put the Flag Enum class outside of CPU class. But I wonder if there is another option so I can keep Flag inside CPU.h
(for logic purposes).
Thanks :)
I have a class called scratch and have used scratch.h to declare it.
Now I have another class called scratch2 under scratch2.h and want to create an object of scratch as a shared pointer.
This is the syntax I used inside scratch2 class declartion:
std::shared_ptr<scratch> newObject(new scratch());
But I am getting this error: Error: Expected type specifier
So I tried this instead:
std::shared_ptr<scratch> newObject2 = std::make_shared<scratch>();
which works fine. Can anyone please tell me why the first one isn't working?
My scratch.h code:
#ifndef _SCRATCH_
#define _SCRATCH_
#include <iostream>
class scratch {
private:
int _a;
float _b;
std::string _s;
public:
scratch();
scratch(int a, float b, std::string n);
~scratch();
};
#endif
and my scratch2.h:
#ifndef _SCRATCH_2_
#define _SCRATCH_2_
#include "scratch.h"
#include <memory>
class scratch2 {
std::shared_ptr<scratch> newObject(new scratch()); // Expected a type specifier error occurs here
std::shared_ptr<scratch> newObject2 = std::make_shared<scratch>(); // works fine here
};
#endif
Because in the context of declaring class members:
std::shared_ptr<scratch> newObject(new scratch());
This initially looks to the compiler as a class method declaration. C++'s syntax is very complicated. You can look at the entire declaration and understand what it's trying to do, but the compiler is parsing keywords one keyword at a time, and sees this:
type name( ...
inside a class declaration, and this starts to look like a class method declaration, and that's what the compiler tried to parse, and failed.
The formal specification of the C++ language spills a lot of ink on the subject of how things should be declared, mindful of the current state of compiler technology.
You need to work with the compiler, and use an alternate syntax that's unambiguous:
std::shared_ptr<scratch> newObject = std::shared_ptr<scratch>(new scratch());
Verified with gcc 5.3
Inside of a class definition, there are only two ways you're allowed to initialize your members. You can use = and you can use {}. You are not allowed to use ():
struct foo {
int x = 4; // OK
int y{7}; // OK
int z(12); // error
};
Admittedly, the compiler error in this case is extremely unhelpful.
Had some issues in my code recently surrounding what I now know of as a Circular dependency. In short there are two classes, Player and Ball, which both need to use information from the other. Both at some point in the code will be passed a reference of the other (from another class that will include both .h files).
After reading up on it, I removed the #include.h files from each one and went with forward declaration. This solved the issue of being able to declare the classes in eachother, but I'm now left with an "Incomplete type error" when trying to access a passed reference to the object. There seem to be a few similar examples around, though often mixed with more complex code and hard to narrow down to the basics.
I've rewritten the code in it's simplest form (a skeleton essentially).
Ball.h:
class Player;
class Ball {
public:
Player& PlayerB;
float ballPosX = 800;
private:
};
Player.h:
class Ball;
class Player {
public:
void doSomething(Ball& ball);
private:
};
Player.cpp:
#include "Player.h"
void Player::doSomething(Ball& ball) {
ball.ballPosX += 10; // incomplete type error occurs here.
}
Any help understanding why this is the case would be greatly appreciated :)
If you will place your definitions in this order then the code will be compiled
class Ball;
class Player {
public:
void doSomething(Ball& ball);
private:
};
class Ball {
public:
Player& PlayerB;
float ballPosX = 800;
private:
};
void Player::doSomething(Ball& ball) {
ball.ballPosX += 10; // incomplete type error occurs here.
}
int main()
{
}
The definition of function doSomething requires the complete definition of class Ball because it access its data member.
In your code example module Player.cpp has no access to the definition of class Ball so the compiler issues an error.
Player.cpp require the definition of Ball class. So simply add #include "Ball.h"
Player.cpp:
#include "Player.h"
#include "Ball.h"
void Player::doSomething(Ball& ball) {
ball.ballPosX += 10; // incomplete type error occurs here.
}
Here is what I had and what caused my "incomplete type error":
#include "X.h" // another already declared class
class Big {...} // full declaration of class A
class Small : Big {
Small() {}
Small(X); // line 6
}
//.... all other stuff
What I did in the file "Big.cpp", where I declared the A2's constructor with X as a parameter is..
Big.cpp
Small::Big(X my_x) { // line 9 <--- LOOK at this !
}
I wrote "Small::Big" instead of "Small::Small", what a dumb mistake..
I received the error "incomplete type is now allowed" for the class X all the time (in lines 6 and 9), which made a total confusion..
Anyways, that is where a mistake can happen, and the main reason is that I was tired when I wrote it and I needed 2 hours of exploring and rewriting the code to reveal it.
In my case it was because a typo.
I had something like
struct SomethingStrcut { /* stuff */ };
typedef struct SomethingStruct smth;
Notice how the name of the structure is not the same one as the type definition.
I misspelled struct to strcut.
Look into your code and see wether you have some typos.
I want to write a static member function in my class CountInv, which should have only this static function and no other members
//Inversions.h
#ifndef INV_H
#define INV_H
#include <string>
#include <vector>
class CountInv
{
static void count();
}
#endif
//Inversions.cpp
#include "Inversions.h"
void CountInv::count() { return; };
I get the following compiler error :
Error 3 error C2556: 'CountInv CountInv::count(void)' :
overloaded function differs only by return type
from 'void CountInv::count(void)' d:\...\inversions.cpp 4
What is wrong? Nowhere have I declared or defined 'CountInv CountInv::count(void)' !! Should I write class c-tors,..,d-tors, or maybe some static data members to return from this function? but this should not be the issue..
Don't forget the closing semicolon ; after your class definition. That I think is causing the obscure compile error.
add ; to the end of class definition everything's goes fine!
I tried this on my local visual studio and adding semicoln in Inversions.h after class definition solves problem.
Thanks
Niraj Rathi
Currently I am trying to get the following code to compile:
terminallog.hh
#ifndef TERMINALLOG_HH
#define TERMINALLOG_HH
#include <string>
#include <sstream>
#include <iostream>
class Terminallog {
public:
Terminallog();
virtual ~Terminallog();
class Warn {
public:
Warn();
private:
bool lineended;
};
friend class Terminallog::Warn;
protected:
private:
Warn warn;
};
terminallog.cc
// stripped code
Terminallog::Terminallog() {
Warn this->warn();
}
Terminallog::Warn::Warn() {
this->lineended = true;
}
//stripped code
Well, as you probably guessed alredy, its failing ;-). My compiler is saying:
g++ src/terminallog.cc inc/terminallog.hh -o test -Wall -Werror
In file included from src/terminallog.cc:8:
src/../inc/terminallog.hh:56: error: declaration of ‘Terminallog::Warn Terminallog::warn’
src/../inc/terminallog.hh:24: error: conflicts with previous declaration ‘void Terminallog::warn(std::string)’
which leaves me out of options. I am obviously doing something wrong, however I have no idea of how to resolve this. I would appreciate any hints.
Thanks in advance
ftiaronsem
Warn this->warn(); is not valid C++ syntax - if you want to initialize the warn member, use an initialization list (you don't need to in this case - the default constructor is called implicitly!).
Terminallog::Terminallog() : warn()
{
// other constructor code
}
// note that `Warn::Warn()` is invoked implicitly on `wake`, so
TerminalLog::Terminallog() {}
// would be equivalent