{"id":2060,"date":"2025-01-27T19:48:51","date_gmt":"2025-01-27T19:48:51","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=2060"},"modified":"2025-01-27T21:19:05","modified_gmt":"2025-01-27T21:19:05","slug":"function-template-overloading","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/function-templates-2\/function-template-overloading\/","title":{"rendered":"Function Template Overloading"},"content":{"rendered":"\n

<\/span>Function Template Overloading<\/span><\/h2>\n\n\n\n

We can declare several function templates with the same name and even declare a combination of function templates and ordinary functions with the same name.<\/p>\n\n\n\n

The compiler needs to perform overload resolution to determine the correct function or template function to invoke.<\/p>\n\n\n\n

Overloading resolution is done as follows:<\/p>\n\n\n\n

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  1. Find the set of function template specializations that will take part in overload resolution, by considering each function template and deciding which template arguments, if any, would be used if no other function templates or functions of the same name were in scope.<\/li>\n\n\n\n
  2. If two template functions can be called and one is more specialized than the other, consider only the most specialized template function<\/li>\n\n\n\n
  3. Do overload resolution for this set of functions, plus any ordinary functions, as for ordinary functions.  If a template function argument has been determined by template argument declaration, that argument cannot have promotions, standard conversions, or user-defined conversions applied.<\/li>\n\n\n\n
  4. If a function and a specialization are equally good matches, the function is preferred.<\/li>\n\n\n\n
  5. If no match is found, the call is in error<\/em>. 
    If there are two or more equally good matches, the call is ambiguous<\/em>.<\/li>\n<\/ol>\n\n\n\n

    For example:<\/p>\n\n\n\n

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    <\/path><\/path><\/svg><\/span>
    \/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Function Overload Resolution<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/13\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n<\/span>\ntemplate<\/span> <<\/span>typename<\/span> <\/span>T<\/span>><\/span><\/span>\nT<\/span> <\/span>max<\/span>(<\/span>T<\/span> <\/span>first<\/span>, <\/span>T<\/span> <\/span>second<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"first  : "<\/span> << <\/span>typeid<\/span>(first).<\/span>name<\/span>() << <\/span>" "<\/span><\/span>\n            << <\/span>"value: "<\/span> << first << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"second : "<\/span> << <\/span>typeid<\/span>(second).<\/span>name<\/span>() << <\/span>" "<\/span><\/span>\n            << <\/span>"value: "<\/span> << second << <\/span>std<\/span>::endl;<\/span><\/span>\n<\/span>\n  T maxValue = first > second ? first : second;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"Max: "<\/span> << maxValue << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>return<\/span> maxValue;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span> <\/span>argv<\/span>[]) <\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>int<\/span> s = <\/span>7<\/span>;<\/span><\/span>\n  <\/span>max<\/span>(<\/span>1<\/span>, <\/span>2<\/span>);<\/span>     \/\/ max<int>(1, 2)<\/span><\/span>\n  <\/span>max<\/span>(<\/span>'a'<\/span>, <\/span>'b'<\/span>);<\/span> \/\/ max<char>('a', 'b')<\/span><\/span>\n  <\/span>max<\/span>(<\/span>2.7<\/span>, <\/span>4.9<\/span>);<\/span> \/\/ max<double>(2.7, 4.9)<\/span><\/span>\n  <\/span>max<\/span>(s, <\/span>7<\/span>);<\/span>     \/\/ max<int>(int(s), 7)<\/span><\/span>\n<\/span>\n  <\/span>max<\/span>(<\/span>'a'<\/span>, <\/span>1<\/span>);<\/span>  \/\/ error: ambiguous<\/span><\/span>\n  <\/span>max<\/span>(<\/span>2.7<\/span>, <\/span>4<\/span>);<\/span>  \/\/ error: ambiguous<\/span><\/span>\n  <\/span><\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
    \n
    which produces the following compile-time errors:<\/p>\n\n\n\n
    main.cpp:31:3 No matching function for call to 'max'\n\nCandidate template ignored: deduced conflicting types for parameter 'T' ('char' vs. 'int')<\/strong>\n\n<\/strong>\nmain.cpp:32:3 No matching function for call to 'max'\n\nCandidate template ignored: deduced conflicting types for parameter 'T' ('double' vs. 'int')<\/strong><\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
    When I remove the offending statements:<\/p>\n\n\n\n
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    \n
    <\/path><\/path><\/svg><\/span>
    \/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Function Overload Resolution<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/13\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n<\/span>\ntemplate<\/span> <<\/span>typename<\/span> <\/span>T<\/span>><\/span><\/span>\nT<\/span> <\/span>max<\/span>(<\/span>T<\/span> <\/span>first<\/span>, <\/span>T<\/span> <\/span>second<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"first  : "<\/span> << <\/span>typeid<\/span>(first).<\/span>name<\/span>() << <\/span>" "<\/span><\/span>\n            << <\/span>"value: "<\/span> << first << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"second : "<\/span> << <\/span>typeid<\/span>(second).<\/span>name<\/span>() << <\/span>" "<\/span><\/span>\n            << <\/span>"value: "<\/span> << second << <\/span>std<\/span>::endl;<\/span><\/span>\n<\/span>\n  T maxValue = first > second ? first : second;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"Max: "<\/span> << maxValue << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>return<\/span> maxValue;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span> <\/span>argv<\/span>[]) <\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>int<\/span> s = <\/span>7<\/span>;<\/span><\/span>\n  <\/span>max<\/span>(<\/span>1<\/span>, <\/span>2<\/span>);<\/span>     \/\/ max<int>(1, 2)<\/span><\/span>\n  <\/span>max<\/span>(<\/span>'a'<\/span>, <\/span>'b'<\/span>);<\/span> \/\/ max<char>('a', 'b')<\/span><\/span>\n  <\/span>max<\/span>(<\/span>2.7<\/span>, <\/span>4.9<\/span>);<\/span> \/\/ max<double>(2.7, 4.9)<\/span><\/span>\n  <\/span>max<\/span>(s, <\/span>7<\/span>);<\/span>     \/\/ max<int>(int(s), 7)<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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    the program produces the following output:<\/p>\n\n\n\n
    first  : i value: 1\nsecond : i value: 2\nMax: 2\nfirst  : c value: a\nsecond : c value: b\nMax: b\nfirst  : d value: 2.7\nsecond : d value: 4.9\nMax: 4.9\nfirst  : i value: 7\nsecond : i value: 7\nMax: 7\nProgram ended with exit code: 0<\/strong><\/code><\/pre>\n\n\n\n
    (See above for mangled type meanings.)<\/p>\n<\/div>\n<\/div>\n\n\n\n
    <\/span>Function Template Overload Resolution<\/span><\/h3>\n\n\n\n
    The ambiguities can be resolved in two ways:<\/p>\n\n\n\n