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Language: C++
Expertise: Intermediate
Oct 19, 1999



Building the Right Environment to Support AI, Machine Learning and Deep Learning

How to Instantiate a Template Correctly

The type that a template takes as an argument must have external linkage. This means that you cannot instantiate a template with a locally-declared type:
int main()
  struct S
      int current_state;
      char description[10];
  } mystruct;

  queue<S> qs;   // 1. compilation error
The line numbered 1 causes a compilation error because it attempts to instantiate a template with a locally-declared type, S. S has no linkage, and as such, it cannot serve as a valid template argument. To fix this, you should move the declaration of struct S outside of main():
struct S
Danny Kalev
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