Why Am I Getting \'Unresolved External Symbol\' Errors in Visual Studio?

Unresolved External Symbol Errors in Object Files

When coding in Visual Studio, you may encounter an "unresolved external symbol" error. This cryptic message can leave developers stumped, unsure where to begin troubleshooting.

This error typically indicates that a function has been declared but not defined. A common scenario is when you include header files (.h) that declare functions but neglect to include the corresponding source files (.cpp) where the functions are defined.

A sample code snippet can illustrate this issue:

<code class="cpp">// A.hpp
class A {
public:
  void myFunc();
};</code>

<code class="cpp">// A.cpp
void A::myFunc() {
  // Function definition
}</code>

In this example, the declaration of myFunc() in A.hpp is separated from its definition in A.cpp. To resolve the error, ensure that you include A.cpp in your project and that the linker can find it when building the executable.

Another potential cause is missing library or dynamic link library (DLL) files. These files contain definitions for functions used in your code. Verify that you have included the appropriate libraries in your project and that they are referenced correctly in the project's build settings.

Finally, ensure that you have correctly defined the class scope for member functions in your .cpp files. Forgetting to include the class selector (e.g., A::) can lead to unresolved symbol errors.

By addressing these common issues, you can resolve "unresolved external symbol" errors and get your program running smoothly.

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