如何修复 C++ 错误：预期的不合格 ID

Question

I'm getting this error on line 6:

 error: expected unqualified-id before '{' token

I can't tell what's wrong.

#include <iostream>

using namespace std;

class WordGame;
{               // <== error is here on line 6
public:

    void setWord( string word )
    {
        theWord = word;
    }
    string getWord()
    {
        return theWord;
    }
    void displayWord()
    {
        cout << "Your word is " << getWord() << endl;
    }
private:
    string theWord;
}


int main()
{
    string aWord;
    WordGame theGame;
    cin >> aWord;
    theGame.setWord(aWord);
    theGame.displaymessage();

}

Answer 1

There should be no semicolon here:

class WordGame;

...but there should be one at the end of your class definition:

...
private:
    string theWord;
}; // <-- Semicolon should be at the end of your class definition

Answer 2

As a side note, consider passing strings in setWord() as const references to avoid excess copying. Also, in displayWord, consider making this a const function to follow const-correctness.

void setWord(const std::string& word) {
  theWord = word;
}

Answer 3

Get rid of the semicolon after WordGame .

You really should have discovered this problem when the class was a lot smaller. When you're writing code, you should be compiling about every time you add half a dozen lines.

Answer 4

Semicolon should be at the end of the class definition rather than after the name:

class WordGame
{
};

Answer 5

For what it's worth, I had the same problem but it wasn't because of an extra semicolon, it was because I'd forgotten a semicolon on the previous statement.

My situation was something like

mynamespace::MyObject otherObject

for (const auto& element: otherObject.myVector) {
  // execute arbitrary code on element
  //...
  //...
} 

From this code, my compiler kept telling me:

error: expected unqualified-id before for (const auto& element: otherObject.myVector) { etc... which I'd taken to mean I'd writtten the for loop wrong. Nope! I'd simply forgotten a ; after declaring otherObject .

Answer 6

For anyone with this situation: I saw this error when I accidentally used my_first_scope::my_second_scope::true in place of simply true , like this:

bool my_var = my_first_scope::my_second_scope::true;

instead of:

bool my_var = true;

This is because I had a macro which caused MY_MACRO(true) to expand into my_first_scope::my_second_scope::true , by mistake, and I was actually calling bool my_var = MY_MACRO(true); .

Here's a quick demo of this type of scoping error:

Program (you can run it online here: https://onlinegdb.com/BkhFBoqUw ):

#include <iostream>
#include <cstdio>

namespace my_first_scope 
{
namespace my_second_scope
{
} // namespace my_second_scope
} // namespace my_first_scope

int main()
{
    printf("Hello World\n");
    
    bool my_var = my_first_scope::my_second_scope::true;
    
    std::cout << my_var << std::endl;

    return 0;
}

Output (build error):

 main.cpp: In function 'int main()': main.cpp:27:52: error: expected unqualified-id before 'true' bool my_var = my_first_scope::my_second_scope::true; ^~~~

Notice the error: error: expected unqualified-id before 'true' , and where the arrow under the error is pointing. Apparently the "unqualified-id" in my case is the double colon ( :: ) scope operator I have just before true .

When I add in the macro and use it (run this new code here: https://onlinegdb.com/H1eevs58D ):

#define MY_MACRO(input) my_first_scope::my_second_scope::input

...

bool my_var = MY_MACRO(true);

I get this new error instead:

 main.cpp: In function 'int main()': main.cpp:29:28: error: expected unqualified-id before 'true' bool my_var = MY_MACRO(true); ^ main.cpp:16:58: note: in definition of macro 'MY_MACRO' #define MY_MACRO(input) my_first_scope::my_second_scope::input ^~~~~