GCC Debugging/g++/Errors

abstract declarator 'TYPE' used as declaration

Message found in GCC version 4.5.1
- often grouped together with:
  - member 'DATA_MEMBER' with constructor not allowed in anonymous aggregate
  - member 'DATA_MEMBER' with destructor not allowed in anonymous aggregate
  - member 'DATA_MEMBER' with copy assignment operator not allowed in anonymous aggregate
a class or struct is missing a name:

struct {  // error, no name
   int bar;
};

a header file has a class or struct with a name already used inside ifndef, define statements

#ifndef foo
#define foo
#include <vector>

struct foo {  // error, foo already in use
   std::vector<int> bar;
};

#endif

call of overloaded 'FUNCTION' is ambiguous

'VARIABLE' cannot appear in a constant-expression

'VARIABLE' cannot be used as a function

Message found in GCC version 4.5.1
make sure the variable name does not have an underscore in it (compiler weirdness)
you're using the same name for a variable name and a function inside a function definition

int foo(int baf) { return baf; }
 
int bar(int foo) {
   foo = foo(4);
   return foo; 
}

conversion from 'TYPE' to non-scalar type 'TYPE' requested

Message found in GCC version 4.5.1
type conversion error, look for missing "::" syntax or missing parenthesis
possibly a casting error
a class member function returns a value that does not match the function's declared return type

class Foo {
public:
   int x;
};
 
class Bar {
public:
   Foo Maz() { return 0; }  // 0 is of type int, not Foo
};

could not convert 'STATEMENT' to 'bool'

Message found in GCC versions 3.2.3, 4.5.1
you a mistyped comparison operator (e.g., using: "=" instead of "==")
you used an incorrect return type for the called function's definition

// you had: 
foo operator<(const foo & f) const

// instead of:
bool operator<(const foo & f) const

you're using an invalid argument for a conditional statement

string x = "foo";
if (x) cout << "true" << endl;

declaration of 'FUNCTION' outside of class is not definition

Message found in GCC versions 3.2.3, 4.5.1
try using '=' to initialize a value instead of parenthesis
you used a semicolon or comma between a constructor and an initializer list instead of a colon
you left a semicolon before the body of a function definition

class Foo 
{
public:
   int bar;
   Foo(int x);
}; 
 
Foo::Foo(int x);  // semicolon ';' needs to be removed
{
   bar = x;
}

declaration of 'VARIABLE' shadows a parameter

Message found in GCC versions 3.2.3, 4.5.1
you're redefining a variable name that's already in use, possibly declared in the function's parameter list

int foo(int bar)
{
   int bar;
   return bar;
}

'TYPE' does not name a type

Message found in GCC version 4.5.1
- in GCC version 3.2.3 sometimes reported as: syntax error before 'CHARACTER' token
- in GCC version 4.0.1, sometimes reported as: ISO C++ forbids declaration
  - e.g.: ISO C++ forbids declaration of 'vector' with no type
you left out an object's name qualifier or using directive

ostream & os;  // instead of: std::ostream & os;

make sure you didn't mistype the scope operator "::", e.g.: "name:name" instead of "name::name"
make sure you included the required libraries

#include <iostream>
// missing vector library include
class Foo {
public:      
   std::vector<int> Bar(std::vector<int> FooBar) { return FooBar; }
};

a header file is listed after a file that makes use of it in the include directives

// test.h file
#ifndef TEST_H_
#define TEST_H_
std::string bar;
#endif

// test.cpp file
#include "test.h"
#include <iostream>  // error, needed before test.h
using namespace std;

int main()
{
   cout << bar << endl;
   return 0;
}

expected 'TOKEN' before 'TOKEN' token

Message found in GCC versions 3.2.3, 4.5.1
- in GCC version 3.2.3 sometimes reported as: syntax error before 'CHARACTER' token
check for a missing comma or parenthesis in a function's parameters
check for a missing semicolon
- e.g.: expected ',' or ';' before 'TOKEN'

const int MAX = 10  // error

int main() {
   string foo;
   cout << foo.size();
   return 0;
}

possibly from a double namespace definition, or a fully-qualified (e.g., std::cout) name already under a 'using' directive
possible missing '<<' or '>>' operator in a cin/cout statement

int foo = 0, bar = 0;
cin foo >> bar;  // should be: cin >> foo >> bar;

expected primary-expression before 'TOKEN'

expected primary-expression before 'int'

Message found in GCC version 4.5.1
- in GCC version 3.2.3 reported as: parse error before ')' token
one likely cause is using (or leaving in) a type name in a function call

int sum(int x, int y) { return (x + y); }

int main() {
   int a = 4, b = 5;
   sum(a, int b); // int is the problem causer
   return 0;
}

expected unqualified-id before

Message found in GCC version 4.5.1
check your syntax for missing, misplaced, or erroneous characters
expected unqualified-id before '(' token
- e.g.: parentheses in a class name

class Foo() {
public:
   int x;
};

expected unqualified-id before 'return'
- e.g.: missing opening brace in a conditional statement

int foo = 3, bar = 2;
if (foo > bar)  // error, no "{"
   cout << foo << endl;
}

incompatible types in assignment of 'TYPE' to 'TYPE'

Message found in GCC versions 4.5.1
you're trying to assign to or initialize a character array using a character pointer
- e.g.: incompatible types in assignment of 'const char*' to 'char [10]'

char bar[10];
const char *foo = "ppp";
bar = *foo;  // error

// possible fix, use strcpy from the cstring header:
char bar[10];
const char *foo = "ppp";
strcpy(bar, foo);

improperly accessing elements of a 2D array

char foo[2][3];
foo[1] = ' '; // error, need both dimensions, eg: foo[1][0] = ' ';

invalid conversion from 'TYPE' to 'TYPE'

Message found in GCC versions 3.2.3, 4.5.1
make sure parentheses were not left out of a function name
make sure you are passing a function the correct arguments

char foo = 'f';
char bar[] = "bar";
if (strcmp(foo, bar) != 0)
   cout << "Correct answer!";
// strcmp was expecting 2 character pointers, foo doesn't qualify

invalid operands of types 'TYPE' and 'TYPE' to binary 'FUNCTION'

Message found in GCC version 4.5.1
You're trying to concatenate to C string arguments with the addition operator

// attempting to combine two C-strings
cout << "abc" + "def";

// possible fix: convert 1 argument to a string type
cout << "abc" + string("def");

invalid use of template-name

invalid use of template-name 'TEMPLATE' without an argument list

Message found in GCC version 4.5.1
- often paired with: expected unqualified-id before 'TOKEN'
- in GCC version 3.2.3 reported as: syntax error before 'CHARACTER' token
the type is missing after the class name in a function definition

template <class T> class Foo {
private:
   int x;
public:
   Foo();
};

template<class T> Foo::Foo() { x = 0; }  // error, should be: Foo<T>::Foo()

is not a member of

Message found in GCC versions 4.5.1
check for a missing header include

example: 'cout' is not a member of 'std'

// test.cpp
// file is missing iostream include directive
int main() {
   std::cout << "hello, world!\n";
   return 0;
}

'TYPE' is not a type

Message found in GCC version 4.5.1
- in GCC version 3.2.3 reported as: type specifier omitted for parameter 'PARAMETER'
you mistyped a template parameter in a function declaration

void foo(int x, vector y);

an included header file does not have the correct libraries included in the source file to implement it:
- e.g.: you're using #include "bar.h" without including the "foo.h" that "bar.h" needs to work
Check that there are no methods with the same name as 'TYPE'.

'CLASS_MEMBER' is private within this context

Message found in GCC versions 3.2.3, 4.5.1
usually reported in the format:
- (LOCATION_OF_PRIVATE_DATA_MEMBER) error: 'DATA_MEMBER' is private
- (LOCATION_OF_CODE_ACCESSING_PRIVATE_DATA) error: within this context
Message usually results from trying to access a private data member of a class or struct outside that class's or struct's definition
Make sure a friend member function name is not misspelled

class FooBar {
private: int bar;
public: friend void foo(FooBar & f);
};
void fooo(FooBar & f) {  // error
   f.bar = 0;
}

make sure a read only function is using a 'const' argument type for the class
make sure functions that alter data members are not const
check for derived class constructors implicitly accessing private members of base classes

class Foo {
private: Foo() {}
public: Foo(int Num) {}
};
class Bar : public Foo {
public: Bar() {}
// Bar() implicitly accesses Foo's private constructor
};

solution 1: use an initializer list to bypass implicit initialization

solution 2: make the accessed base class member protected instead of private

You're trying to initialize a contained class member by accessing private data

class Foo {
private: char mrStr[5];
public: Foo(const char *s = "blah") { strcpy(mrStr, s); }
};

class Bar {
private:
   int mrNum;
   Foo aFoo;
public:
   Bar(int n, const Foo &f);
};

// error, attempting to use the Foo class constructor by accessing private data:
Bar::Bar(int n, const Foo &f) : aFoo(f.mrStr) {  // mrStr is private
   mrNum = n;
}

possible fix, assign the whole object rather than part of it:

Bar::Bar(int n, const Foo &f) : aFoo(f) {
   mrNum = n;
}

ISO C++ forbids declaration of 'FUNCTION' with no type

Message found in GCC version 3.2.3, 4.5.1
you've created a function with no listed return type

Foo() { return 0: }
// should be: int Foo() { return 0: }

multiple definitions of

eg: multiple definition of `main'

Message found in GCC version 4.5.1
check for missing inclusion guard in header file
check for duplicate file listing in compile commands / makefile
- e.g.: g++ -o foo foo.cpp foo.cpp
check for definitions rather than only declarations in the header file

'CLASS FUNCTION(ARGUMENTS)' must have an argument of class or enumerated type

Message found in GCC versions 3.2.3, 4.5.1
you're attempting to access members of a class with a non-member function
- non-member functions must access class members explicitly

eg: CLASS_NAME FUNCTION_NAME(CLASS_NAME OBJECT_NAME, ARGUMENTS)

you're redefining an operator for a standard (built-in) type

class Foo {
public:
   friend int operator+(int x, int y);
};

new types may not be defined in a return type

Message found in GCC version 4.5.1
- in GCC version 3.2.3, reported as:

semicolon missing after definition of 'CLASS'

ISO C++ forbids defining types within return type

check for a missing semicolon at the end of a class definition

class Foo {
public:
   int x;
}  // Error

no match for call to 'FUNCTION'

Message found in GCC versions 3.2.3, 4.5.1
make sure the function's namespace is used ( using namespace std / std::function() )
make sure the function name is not misspelled, parentheses aren't missing
make sure the function is called with the correct arguments / types / class
if you're initializing a variable via parentheses, if there's underscores in the variable name try removing them. Sometimes an equals sign is the only way...
you're using the same name for a variable and a function within the same namespace

string bar() {
   string foo = "blah";
   return foo;
}

int main() {
   string bar;
   bar = bar();  // error, "bar()" was hidden by string initialization
   return 0;
}

no matching function for call to 'FUNCTION'

Message found in GCC version 4.5.1
make sure there aren't parentheses where there shouldn't be (e.g.: classname::value() instead of classname::value )
you're using a string argument with a function that expects a C-string

// broken code
ifstream in;
string MrString = "file.txt";
in.open(MrString);

// solution: convert the string to a C-string
ifstream in;
string MrString = "file.txt";
in.open(MrString.c_str());

non-constant 'VARIABLE' cannot be used as template argument

Message found in GCC version 3.2.3
- in GCC version 4.5.1 reported as: 'VARIABLE' cannot appear in a constant-expression
variable used for a template argument, which are required to be constant at compile time

template <class T, int num>
class Bar {
private:
   T Foo[num];
};

int main() {
   int woz = 8;
   Bar<double, woz> Zed;  // error, woz is not a constant
   return 0;
}

non-member function 'FUNCTION' cannot have cv-qualifier

error: non-member function 'int Foo()' cannot have cv-qualifier

cv = constant / volatile

Message found in GCC version 4.5.1
you're using the 'post' const (constant value) on a non-member function
you're not using the scope qualifier ("TYPENAME::") in the function definition
you mistyped the definition for a template class's member function

template<class Type>
class Foo {
private:
   int stuff;
public:
   int bar() const;
};

template<class Type>
int Foo::bar() const {  // error
   return stuff;
}

possible fix:

template<class Type>
int Foo<Type>::bar() const {
   return stuff;
}

passing 'const OBJECT' as 'this' argument of 'FUNCTION' discards qualifiers

Message found in GCC version 4.5.1
you're returning an address
you're attempting to access a container element with a const_iterator using a member function that has no non-const versions. The non-const function does not guarantee it will not alter the data

request for member 'NAME' in 'NAME', which is of non-class type 'CLASS'

Message found in GCC versions 4.5.1
- in GCC version 3.2.3 reported as:

request for member 'NAME' in 'NAME', which is of non-aggregate type 'TYPE'

check the function call in the code, it might be calling a function with incorrect arguments or it might have misplaced/missing parenthesis
your using the "*this" pointer where you should just be using the functions name
e.g., use: return mem_func(); instead of: return *this.mem_func();
using the "*this" pointer with the wrong syntax

class Foo {
public:
   int x;
   Foo(int num = 0) { x = num; }
   void newX(int num);
};

void Foo::newX(int num) {
   *this.newX(num);  // error, need (*this).newX or this->newX
}

statement cannot resolve address of overloaded function

Message found in GCC versions 3.2.3, 4.5.1
make sure you're not forgetting the parenthesis after a member function name

class Foo {
public:
   int Bar() { return 0; }
};

int main() {
   Foo x;
   x.Bar;  // error
   return 0;
}

two or more data types in declaration of 'NAME'

Message found in GCC version 4.5.1
- in GCC version 3.2.3 reported as: extraneous 'TYPE' ignored
you have multiple data types listed for a function declaration's return value

int char sum(int x, int y);  // int char

possibly a missing semicolon in between 2 type declarations
- usually missing in a function, struct, or class declaration after the curly braces {}

<GOBBLEDEGOOK> undefined reference to <GOBBLEDEGOOK>

Message found in GCC version 4.5.1
- in GCC versions 4.0.1, 4.2.1 reported as: Undefined symbols
check for a missing or mistyped header includes
check for a missing or mistyped files/libraries in a project/make file
check for a missing, mistyped, or undefined functions or class constructors

// header file
void foo();
void bar();
void baz();

// implementation file, bar definition is missing
void foo() { cout << "foo\n"; }
void baz() { cout << "baz\n"; }

check for function declarations that do not match their definitions
make sure function names do not overlap those in existing header files
make sure compile commands syntax / makefile structure is correct (e.g.: g++ -o file.cc ... etc.)
no main() function is defined in any of the files inside a project/makefile
- e.g.: undefined reference to `WinMain@16'

'NAME' was not declared in this scope

Message found in GCC version 4.5.1
- in GCC versions 3.2.3 reported as: 'FUNCTION' undeclared (first use of this function)
look for a misspelled or changed variable/function/header call name

lonh wait;

// instead of:
long wait;

make sure the proper header and library files are included
- defined variables may need the headers they utilize included in all files that use the defined variables