My professor gave me the following .h file as part of a programming assignment to make a lexer.
#ifndef LEXER_H
#define LEXER_H
#include "token.h"
#include <istream>
class Lexer {
public:
Lexer(std::istream& input_stream);
Token next_token();
private:
int current_line;
int current_column;
std::istream& input_stream;
};
#endif
I started making the .cpp file as shown below:
#include "lexer.h"
Lexer::Lexer(std::istream& inputstream){
}
When I try to compile, I get the error message:
lexer.cpp: In constructor ‘Lexer::Lexer(std::istream&)’:
lexer.cpp:4: error: uninitialized reference member ‘Lexer::input_stream’
The compiler is explicit : a reference member must be initialized in the member initialization list :
Lexer::Lexer(std::istream& inputstream) : input_stream(inputstream) {
}
Related
I am new to C++ programming and have a compiler error that I can't figure out. Any help would be appreciated.
Here is the build log:
C:\Dev\MemberTest\Entity.cpp|6|error: redefinition of 'class Entity::Entity'|
C:\Dev\MemberTest\Entity.h|6|error: previous definition of 'class Entity::Entity'|
||=== Build failed: 2 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|
The program has Main.cpp, Entity.h and Entity.cpp (I was just tinkering with how to implement headers and source files).
#include <iostream>
#include "Entity.h"
int main()
{
Entity::Entity Person("Grant", true); //Create person and set membership
std::cout << Person.getName() << " is a member: " << Person.getMembership() << std::endl;
return 0;
}
#ifndef ENTITY_H_INCLUDED
#define ENTITY_H_INCLUDED
namespace Entity
{
class Entity
{
private:
std::string name;
bool member;
public: //Get, set, constructor calls for a bool and string.
Entity(std::string y, bool x);
bool getMembership();
std::string getName();
void setMembership(bool x);
};
}
#endif // ENTITY_H_INCLUDED
#include <string>
#include "Entity.h"
namespace Entity
{
class Entity
{
private:
std::string name;
bool membership;
public:
Entity(std::string y, bool x):name(y),membership(x){}
bool getMembership(){return this->membership;};
std::string getName(){return this->name;};
void setMembership(bool x){this->membership=x;};
};
}
I've looked around for a solution and found questions like this: error: redefinition of class but the solutions I'm seeing aren't relevant to my program because I'm already using #ifndef.
Since I'm not sure what other info might be needed here goes: All three files are in the same folder and there aren't other source or header files in that folder. Oddly enough if I comment out the #include "Entity.h" in the Entity.cpp file and reference the source in Main.cpp instead of Entity.h it compiles and runs fine. I'm coding on Code::Blocks and with the GCC Compiler. Thanks again for any help.
The implementation file (Entity.cpp) should not contain the class definition again. Instead, you write non-inline definitions ("out of class"):
#include <string>
#include "Entity.h"
namespace Entity
{
Entity::Entity(std::string y, bool x) : name(y), membership(x) {}
bool Entity::getMembership() { return membership; }
std::string Entity::getName() { return name; }
void Entity::setMembership(bool x) { membership = x; }
}
Also note that your Entity.h header depends on std::string which requires the #include <string> header there, not just in the implementation file (Entity.cpp). There is no need to use this-> here nor some of the semicolons (;).
Oddly enough if I comment out the #include "Entity.h" in the Entity.cpp file and reference the source in Main.cpp instead of Entity.h it compiles and runs fine
That is because you can define functions inline in the class (instead of putting them in the implementation file). What you did is implement all of them in the class definition, and therefore you don't need an implementation file anymore.
In other words, your Entity.cpp looked like a header file with a full implementation of the class, although you called it .cpp rather than .h. Thus if you include that file, it would work.
I'm creating a class called person right now in separate header and cpp files.
And for one of the functions I'm getting this error:
declaration is incompatible with "Person::stat Person::getStat()" (declared at line 26 of "C:...")
(Not the exact directory but you get the idea)
Here is the code in the header file:
#pragma once
#include <string>
#include <iostream>
class Person
{
public:
struct stat {
int str;
int end;
int dex;
int intel;
};
Person();
~Person();
//properties
stat getStat();
};
Here is the code in the cpp file:
#include "pch.h"
#include "Person.h"
#include <string>
#include <iostream>
Person::Person()
:age(12), height(0)
{
}
Person::~Person()
{
}
struct stat Person::getStat() {
}
I'm getting the error with the getStat() function. I've tried including the string and iostream headers in both file and also only in the header file since a similar post suggested it. Both didn't solve my problem however.
Should be
Person::stat Person::getStat() {
}
Your version declares a new struct stat which isn't the same as Person::stat.
struct stat Person::getStat() is a method that returns a stat that belongs to the global namespace, not to Person:
Person::stat Person::getStat()
Note that there is no struct here (to avoid declaring one). In C++, we don't use struct after the type has been declared.
I have implemented a class buffer_manger.The header file (.hpp) and (.cpp) files are given below.
buffer_manager.hpp
#ifndef BUFFER_MANAGER_H
#define BUFFER_MANAGER_H
#include <iostream>
#include <exception>
#include <boost/array.hpp>
#include <boost/algorithm/hex.hpp>
#include <algorithm>
#include <iomanip>
class buffer_manager
{
public:
typedef boost::array<unsigned char, 4096> m_array_type;
m_array_type recv_buf;
buffer_manager();
~buffer_manager();
std::string message_buffer(m_array_type &recv_buf);
m_array_type get_recieve_array();
private:
std::string message;
};
#endif //BUFFER_MANAGER_H
buffer_manager.cpp
#include <iostream>
#include <boost/array.hpp>
#include <boost/algorithm/hex.hpp>
#include <algorithm>
#include "buffer_manager.hpp"
buffer_manager::buffer_manager()
{
}
buffer_manager::~buffer_manager()
{
}
std::string buffer_manager::message_buffer(m_array_type &recv_buf)
{
boost::algorithm::hex(recv_buf.begin(), recv_buf.end(), back_inserter(message));
return message;
}
m_array_type buffer_manager::get_recieve_buffer()
{
return recv_buf;
}
The problem is I have defined a type m_array_type insde the class buffer_manager. I have also declared a variable of that type named recv_buf
I tried to implement an accessor function for that member variable. I get the error that
buffer_manager.cpp:22:1: error: ‘m_array_type’ does not name a type
m_array_type buffer_manager::get_recieve_buffer()
How do I get the buffer_manager.cpp to recognize the type m_array_type
You simply need to qualify it:
buffer_manager::m_array_type buffer_manager::get_recieve_buffer()
^^^^^^^^^^^^^^^^
{
return recv_buf;
}
Everything after the member function name will get looked up in the context of the class, but not the return type.
As a side-note, do you really want to return it by-value? Perhaps m_array_type&?
m_array_type buffer_manager::get_recieve_buffer()
The problem here is that when the compiler sees m_array_type it doesn't know that it's compiling a member function. So you have to tell it where that type is defined:
buffer_manager::m_array_type buffer_manager::get_recieve_buffer()
This question already has answers here:
Can standard container templates be instantiated with incomplete types?
(3 answers)
Closed 8 years ago.
I defined two header files.
global.h
#ifndef GLOBAL_H
#define GLOBAL_H
#include <queue>
#include <string>
//#include "token.h"
class Token;
typedef std::string TokenValue;
enum TokenType{//...};
inline void clear(std::queue<Token> tokens)
{
std::queue<Token> empty;
std::swap(tokens, empty);
}
#endif // GLOBAL_H
and token.h
#ifndef TOKEN_H
#define TOKEN_H
#include "global.h"
class Token
{
public:
Token (TokenType token_type, TokenValue token_value)
{
token_type_ = token_type;
token_value_ = token_value;
}
~Token (){}
//...
private:
TokenType token_type_;
TokenValue token_value_;
};
I use foward declaration in global.h, but i don't use the reference or pointer of class Token. I use std::queue<Token> empty; in global.h. I think this statement must need the size of Token. I can't figure out why it can compiles success. It's the problem of queue?
When you include global.hin token.h the compiler has the complete information to work. Try to include global.h in another file and you will have your compile error :-)
I got three .cpp files and two header files.
But when i compile them, meaning the Point.cpp, Data.cpp and main.cpp, it will say
Data.h:6:7 redefinition of Data at 'Data.h'
Data.h:6:7 previously definition of 'class Data'
Below is my Data.h(previously known as 2.h at above)
#include <iostream>
#include <string>
using namespace std;
class Data
{
private:
string sType;
public:
Data();
Data(string);
void setSType(string);
string getSType();
};
Below is my data.cpp
#include "Data.h"
Data::Data()
{
sType = "";
}
Data::Data(string s)
{
sType = s;
}
void Data::setSType(string ss)
{
sType = ss;
}
string Data::getSType()
{
return sType;
}
Below is my PointD.h (previously known as 3.h)
#include <iostream>
#include <string>
#include "Data.h"
using namespace std;
class PointD
{
private:
int x
Data data1;
public:
PointD();
PointD(int,Data);
void setX(int);
void setData(Data);
int getX();
Data getData();
};
Below is my PointD.cpp
#include "PointD.h"
PointD::PointD()
{
x = 0;
}
PointD::PointD(int xOrdinate,Data dd)
{
x = xOrdinate;
data1 = dd;
}
void PointD::setXordinate(int Xordinate)
{
x = Xordinate;
}
void PointD::setData(Data dd)
{
data1 = dd;
};
int PointD::getXordinate()
{
return x;
}
Data PointD::getData()
{
return data1;
}
This is my main.cpp
#include <iostream>
#include <string>
#include "Data.h"
#include "PointD.h"
using namespace std;
int main()
{
const int MAX_NUM = 20;
Data ldata[MAX_NUM];
PointD pointd[MAX_NUM];
//more codes..
}
But when i compile them, meaning the Point.cpp, Data.cpp and main.cpp, it will say
Data.h:6:7 redefinition of Data at 'Data.h'
Data.h:6:7 previously definition of 'class Data'
Can anybody let me know whats actually went wrong here..
You need to use include guards, or the easiest:
#pragma once
in your header files
See Purpose of Header guards for more background
Idea: 1.hpp
#ifndef HEADER_GUARD_H1_HPP__
#define HEADER_GUARD_H1_HPP__
// proceed to declare ClassOne
#endif // HEADER_GUARD_H1_HPP__
In each of your header files write:
#ifndef MYHEADERNAME_H
#define MYHEADERNAME_H
code goes here....
#endif
Its better like this:
#ifndef DATA_H /* Added */
#define DATA_H /* Added */
#include <iostream>
#include <string>
// using namespace std; /* Removed */
class Data
{
private:
std::string sType;
public:
Data();
Data( std::string const& ); // Prevent copy of string object.
void setSType( std::string& ); // Prevent copy of string object.
std::string const& getSType() const; // prevent copy on return
std::string& getSType(); // prevent copy on return
};
#endif /* DATA_H */
The big fix is adding ifndef,define,endif. The #include directive works as if copying and pasting the .h to that line. In your case the include from main.cpp are:
main.cpp
-> Data.h (1)
-> Point.h
-> Data.h (2)
At (2), Data.h has already been `pasted' into main.cpp at (1). The class declaration of Data, i.e. "class Data{ .... };" , appears twice. This is an error.
Adding include guards to the top and bottom of every .h are standard practice to avoid this problem. Don't think about it. Just do it.
Another change I'd suggest is to remove any "using namespace ..." lines from any .h . This breaks the purpose of namespaces, which is to place names into separate groups so that they are not ambiguous in cases where someone else wants an object or function with the same name. This is not an error in your program, but is an error waiting to happen.
For example, if we have:
xstring.h:
namespace xnames
{
class string
{
...
};
}
Foo.h
#include <xstring>
using namespace xnames;
...
test.cxx:
#include "Foo.h"
#include "Data.h" // Breaks at: Data( string ); -- std::string or xnames::string?
...
void test()
{
string x; // Breaks. // std::string or xnames::string?
}
Here the compiler no longer knows whether you mean xnames::string or std::string. This fails in test.cxx, which is fixable by being more specific:
void test()
{
std::string x;
}
However, this compilation still now breaks in Data.h. Therefore, if you provide that header file to someone, there will be cases when it is incompatible with their code and only fixable by changing your header files and removing the "using namespace ...;" lines.
Again, this is just good coding style. Don't think about it. Just do it.
Also, in my version of Data.h, I've changed the method parameters and return types to be references (with the &). This prevents the object and all of its state from being copied. Some clever-clogs will point our that the string class's is implementation prevents this by being copy-on-write. Maybe so, but in general, use references when passing or returning objects. It just better coding style. Get in the habit of doing it.