#Concept #Study #CPP
When building a project inside C++, the compiler is building usually only the necessary files that were modified.
To override this, you need to `rebuild` the project, which will [[Clean in C++]] and `build` all of the files again.
## Linker errors
is thrown when linking the objects/files to machine code fails during building.
An example for a linker error is when trying to use librarys or anything else referencing other parts that are not included at the beginning.
```
// Example for a linker error
#include <iostream>
extern int x; // trying to define the variable x from extern, which is not included/imported
int main(){
std::cout << x;
return 0
}
// linker error: undefined reverence to 'x'
```
## 🔗Resources