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C++ Debugging Tips

You should also review the C debuggging tips as some errors C & C++ have in common.

Note: if you get a lot of compile errors/warnings, resolve them from first to last. C++ can generate a lot of errors and warnings, many of which are not particuarly helpful.

Compile Errors

undefined references

undefined reference to `std::ostream::operator<<(std::ostream)'
undefined reference to `std::cout'

This can happen if you use gcc instead of g++ to compile your C++ program. If the undefined reference is to a class you write, you may have left of the scope resolution operator from the method definiton.

string does not name a type

myfile.hpp:32:5: error: 'string' does not name a type; did you mean 'stdin'?
    string mystr;

This indicates that the compiler doesn’t know what namespace “string” is in. Use std::string or add using namespace std to the top of the file.

request for member in non-class type

non_class_type.cpp:18:14: error: request for member ‘print’ in ‘greeting’, which is of non-class type ‘MyClass()’
   18 |     greeting.print();

In this case, MyClass likely has a constructor with no parameters, but the variable greeting is declared with empty parenthesis, as follows:

MyClass greeting();

But the correct declaration of a MyClass object with no parameters would be without any parenthesis, as follows:

MyClass greeting;

default argument given for parameter

error: default argument given for parameter

This happens when you have default parameters on both the declaration & definition. Only one or the other can have defaults.

Undefined symblols for architecture x86_64

Undefined symbols for architecture x86_64:
  "MyClass::myMethod()", referenced from:
      _main in myprog-32196b.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Notice from the error that it doesn’t know what myMethod() is. This means it is declared or used without being defined. Usually, this is a result of one of the following:

  • The cpp file with myMethod()’s definition (likely myclass.cpp) is not included in the compile line.
    gcc --std=c++17 myprog.cpp myclass.cpp
  • The method myMethod is not properly defined anywhere. This is usually the result of defining the method without the scope resolution operator to indicate which class it belongs to.

class has no member

error: ‘class myClass has no member named 'someThing'

myClass does not have a someThing defined. Either you forgot to add someThing, the object isn’t of the correct type, or you have a typo in the name of the variable.

no operator found which taxes a right-hand operand of type

error C2679: binary '<<': no operator found which takes a right-hand operand of type 'Movie'

You can’t print a user-defined class using cout << unless you override the << operator [operator<<]. You can also print each individual field using cout.

expected ; before string constant

program.cpp: In member function 'void MyClass::print()':
program.cpp:87:19: error: expected ';' before string constant
              cout "R = " << r << ": ";

This is because there is no << before the cout.