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      std::ranges::fill

      From cppreference.com
      <cpp‎ |algorithm‎ |ranges
       
       
      Algorithm library
      Constrained algorithms and algorithms on ranges(C++20)
      Constrained algorithms, e.g.ranges::copy,ranges::sort, ...
      Execution policies(C++17)
      Sorting and related operations
      Partitioning operations
      Sorting operations
      Binary search operations
      (on partitioned ranges)
      Set operations (on sorted ranges)
      Merge operations (on sorted ranges)
      Heap operations
      Minimum/maximum operations
      (C++11)
      (C++17)
      Lexicographical comparison operations
      Permutation operations
      C library
      Numeric operations
      Operations on uninitialized memory
       
      Constrained algorithms
      All names in this menu belong to namespacestd::ranges
      Non-modifying sequence operations
      Modifying sequence operations
      Partitioning operations
      Sorting operations
      Binary search operations (on sorted ranges)
             
             
      Set operations (on sorted ranges)
      Heap operations
      Minimum/maximum operations
      Permutation operations
      Fold operations
      Operations on uninitialized storage
      Return types
       
      Defined in header<algorithm>
      Call signature
      (1)
      template<class T,std::output_iterator<const T&> O,std::sentinel_for<O> S>
      constexpr O fill( O first, S last,const T& value);
      (since C++20)
      (until C++26)
      template<class O,std::sentinel_for<O> S,class T=std::iter_value_t<O>>

      requiresstd::output_iterator<O,const T&>

      constexpr O fill( O first, S last,const T& value);
      (since C++26)
      (2)
      template<class T,ranges::output_range<const T&> R>
      constexprranges::borrowed_iterator_t<R> fill( R&& r,const T& value);
      (since C++20)
      (until C++26)
      template<class R,class T=ranges::range_value_t<R>>

      requiresranges::output_range<R,const T&>

      constexprranges::borrowed_iterator_t<R> fill( R&& r,const T& value);
      (since C++26)
      1) Assigns the givenvalue to the elements in the range[firstlast).
      2) Same as(1), but usesr as the source range, as if usingranges::begin(r) asfirst andranges::end(r) aslast.

      The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:

      Contents

      [edit]Parameters

      first, last - the iterator-sentinel pair defining therange of elements to modify
      r - the range of elements to modify
      value - the value to be assigned

      [edit]Return value

      An output iterator that compares equal tolast.

      [edit]Complexity

      Exactlylast- first assignments.

      [edit]Possible implementation

      struct fill_fn{template<class O,std::sentinel_for<O> S,class T=std::iter_value_t<O>>    requiresstd::output_iterator<O,const T&>constexpr O operator()(O first, S last,const T& value)const{while(first!= last)*first++= value; return first;} template<class R,class T=ranges::range_value_t<R>>    requiresranges::output_range<R,const T&>constexprranges::borrowed_iterator_t<R> operator()(R&& r,const T& value)const{return(*this)(ranges::begin(r),ranges::end(r), value);}}; inlineconstexpr fill_fn fill;

      [edit]Notes

      Feature-test macroValueStdFeature
      __cpp_lib_algorithm_default_value_type202403(C++26)List-initialization for algorithms(1,2)

      [edit]Example

      Run this code
      #include <algorithm>#include <complex>#include <iostream>#include <vector> void println(constauto& seq){for(constauto& e: seq)std::cout<< e<<' ';std::cout<<'\n';} int main(){std::vector<int> v{0,1,2,3,4,5}; // set all elements to -1 using overload (1)    std::ranges::fill(v.begin(), v.end(),-1);    println(v); // set all element to 10 using overload (2)    std::ranges::fill(v,10);    println(v); std::vector<std::complex<double>> nums{{1,3},{2,2},{4,8}};    println(nums);#ifdef __cpp_lib_algorithm_default_value_type        std::ranges::fill(nums,{4,2});// T gets deduced#else        std::ranges::fill(nums,std::complex<double>{4,2});#endif    println(nums);}

      Output:

      -1 -1 -1 -1 -1 -110 10 10 10 10 10(1,3) (2,2) (4,8)(4,2) (4,2) (4,2)

      [edit]See also

      assigns a value to a number of elements
      (algorithm function object)[edit]
      copies a range of elements to a new location
      (algorithm function object)[edit]
      saves the result of a function in a range
      (algorithm function object)[edit]
      applies a function to a range of elements
      (algorithm function object)[edit]
      fills a range with random numbers from a uniform random bit generator
      (algorithm function object)[edit]
      copy-assigns the given value to every element in a range
      (function template)[edit]
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