MSVC build errors > C2065

C2065: undeclared identifier

error C2065: 'cout': undeclared identifier

The compiler met a name it has no declaration for at that point of the file.

Causes and fixes

1. The name is misspelled. C++ is case-sensitive: Count and count are different names.
2. The header that declares it is not included. Include it in the file that uses the name, instead of relying on another header to include it.
3. The name lives in a namespace. Write std::cout, or add a using declaration.
4. The declaration is in another scope, or comes later. A variable declared inside a block or a loop does not exist after it, and a name must be declared before its first use.
5. Code comes before the precompiled header. With precompiled headers, everything before #include "pch.h" is ignored. Make it the first line of the file.
6. The declaration is excluded by the preprocessor. Check the #if or #ifdef around it and the preprocessor definitions of the configuration.

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Related errors: C2039, C4430, C1083, C1010. See all guides.