C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 35:
35.1 What's the idea behind templates?
35.2 What's the syntax / semantics for a "class template"?
35.3 What's the syntax / semantics for a "function template"?
35.4 How do I explicitly select which version of a function template should get called?
35.5 What is a "parameterized type"?
35.6 What is "genericity"?
35.7 My template function does something special when the template type T is int or std::string; how do I write my template so it uses the special code when T is one of those specific types?
35.8 Huh? Can you provide an example of template specialization that doesn't use foo and bar?
35.9 But most of the code in my template function is the same; is there some way to get the benefits of template specialization without duplicating all that source code?
35.10 All those templates and template specializations must slow down my program, right?
35.11 So templates are overloading, right?
35.12 Why can't I separate the definition of my templates class from its declaration and put it inside a .cpp file?
35.13 How can I avoid linker errors with my template functions? Updated!
35.14 How does the C++ keyword export help with template linker errors? Updated!
35.15 How can I avoid linker errors with my template classes? Updated!
35.16 Why do I get linker errors when I use template friends?
35.17 How can any human hope to understand these overly verbose template-based error messages?
35.18 Why am I getting errors when my template-derived-class uses a nested type it inherits from its template-base-class?
35.19 Why am I getting errors when my template-derived-class uses a member it inherits from its template-base-class?
35.20 Can the previous problem hurt me silently? Is it possible that the compiler will silently generate the wrong code?
35.21 How can I create a container-template that allows my users to supply the type of the underlying container that actually stores the values?
35.22 Follow-up to previous: can I pass in the underlying structure and the element-type separately?
35.23 Related: all those proxies must negatively reflect on the speed of my program. Don't they?
[35.3] What's the syntax / semantics for a "function template"?

Consider this function that swaps its two integer arguments:

void swap(int& x, int& y)
{
  int tmp = x;
  x = y;
  y = tmp;
}
If we also had to swap floats, longs, Strings, Sets, and FileSystems, we'd get pretty tired of coding lines that look almost identical except for the type. Mindless repetition is an ideal job for a computer, hence a function template:
template<typename T>
void swap(T& x, T& y)
{
  T tmp = x;
  x = y;
  y = tmp;
}
Every time we used swap() with a given pair of types, the compiler will go to the above definition and will create yet another "template function" as an instantiation of the above. E.g.,
int main()
{
  int         i,j;  /*...*/  swap(i,j);  // Instantiates a swap for int
  float       a,b;  /*...*/  swap(a,b);  // Instantiates a swap for float
  char        c,d;  /*...*/  swap(c,d);  // Instantiates a swap for char
  std::string s,t;  /*...*/  swap(s,t);  // Instantiates a swap for std::string
  ...
}
Note: A "template function" is the instantiation of a "function template".