MSVC: error C2065: 'x': undeclared identifier

Meaning

This is MSVC's counterpart of GCC's "was not declared in this scope". With precompiled headers a missing #include "pch.h" first line, a header only included in some configurations, and a wrong _MSC_VER or #ifdef guard are extra causes. Often followed by C3861 ("identifier not found") for functions.

Common causes

• Missing #include of the header that declares the name
• Missing std:: qualifier or using declaration
• Typo or wrong case in the name
• Variable declared in an inner scope or later in the file
• #include "pch.h" missing as the first line of a .cpp in a project with precompiled headers

Detailed fix by platform

Code examples

#include <string>
#include <iostream>        // without this: error C2065: 'cout': undeclared identifier

int main() {
    std::string name = "Ada";
    std::cout << name << "\n";
}

How to diagnose

1. Header — Which header declares it?
2. Scope — Used where it is visible?
3. PCH — Precompiled header include first?

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