C++ - Template function using initializer_list as a parameter

Question

I wrote a simple function to calculate the min value of an std::initializer_list like this:

template<typename T> inline T min(const std::initializer_list<T>& values) { T minValue = values[0]; for ( const auto& v : values ) if ( v < minValue ) minValue = v; return minValue; }

But I get the following errors:

error C2027: use of undefined type 'T'
error C2226: syntax error: unexpected type 'std::initializer<_Elem>'
error C2988: unrecognizable template declaration/definition
error C2059: syntax error: ')'
error C2143: syntax error: missing ';' before 'identifier'

I tried to change the std::initializer_list with an std::vector and there were no errors. Does this mean that we cannot define a template function using std::initializer_list as a parameter? I am using Visual Studio 2013.

Please provide a minimal reproducible example. Note that initializer_list doesn't have operator[]. Note also that std::min exists. — Barry
– Barry, Commented Oct 17, 2016 at 15:08
@Barry There is nothing else to provide this is the exact code that gives these errors. Without even calling min() function — DimChtz
– DimChtz, Commented Oct 17, 2016 at 15:09
@Barry This min is inside a different namespace. And even if I remove everything inside the function and just return T(); I still get the same errors — DimChtz
– DimChtz, Commented Oct 17, 2016 at 15:10

rocambille · Accepted Answer · 2016-10-17 15:13:27Z

3

Looking in the documentation, std::initializer_list has no operator[], so this line:

T minValue = values[0];

can not be valid. You can replace it with:

T minValue = *values.begin();

edited Oct 17, 2016 at 15:13

answered Oct 17, 2016 at 15:12

rocambille

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4 Comments

DimChtz Over a year ago

Thanks for your answer. I still get the same errors

rocambille Over a year ago

I tested the code in rextester.com with visual compiler. It is working with a main function just executing std::cout << (min({1, 2, 3}));. You should edit your question with a complete example

rocambille Over a year ago

Did you include <initializer_list>?

jaggedSpire Over a year ago

@wasthishelpful he said he did in the comments on the question.

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