class and pass string as argument to method - c++

Question

How to pass a string to a method in a class?
code
class Txtbin{
private:
std::string input;
std::string output = "output.png";
void error();
public:
Txtbin();
void run();
};
Txtbin::Txtbin(){
}
void Txtbin::error(const char* str){
throw std::runtime_error(str);
}
void Txtbin::run(){
if(input == ""){
error("Input file not defined");
}
}
error
# g++ -std=c++11 txtbin.cpp -o txtbin `pkg-config opencv --cflags --libs`
txtbin.cpp:30:6: error: prototype for ‘void Txtbin::error(const char*)’ does not match any in class ‘Txtbin’
void Txtbin::error(const char* str){
^
txtbin.cpp:14:8: error: candidate is: void Txtbin::error()
void error();
^

Answer 1

As others mentioned, you are declaring void error(); but defining void error(const char* str);. Put const char* str parameter in the declaration too, inside the class.

Answer 2

prototype for ‘void Txtbin::error(const char*)’
does not match any in class ‘Txtbin’
You're trying to define Txtbin's void error(const char*) function, but it does not have one.
candidate is: void Txtbin::error()
It does, however, declare a void error() function, without the parameter. Since you actually use that parameter in the implementation, you probably want to add it to its declaration.

Answer 3

Like others have said, void error() requires no parameter. However later you create void error(const char* str) which has a parameter.
class Txtbin{
private:
string input;
string output = "output.png";
public:
Txtbin();
void error(const char*); //This is what you need.
/* void error(); THIS IS WHAT YOU HAD */
void run();
};
void Txtbin::error(const char* str)
{
//Whatever
}