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POc++ - ‘function’ in namespace ‘std’ does not name a type
 

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  1. POc++ - ‘function’ in namespace ‘std’ does not name a type
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    <p>main.cc:</p> <pre><code>#include &lt;cstdio&gt; #include &lt;functional&gt; #include "segtree.h" // NOLINT int main() { const int n = 8; SegmentTree&lt;int&gt; segmentTree(n, 1, std::multiplies&lt;int&gt;()); for (int i = 0; i &lt; n; ++i) segmentTree.set(i, i + 1); for (int i = 0; i &lt; n; ++i) for (int j = i; j &lt; n; ++j) { int s = segmentTree.get(i, j); std::printf( "Function applied from data[%d] to data[%d] is equal to %d \n", i, j, s); } return 0; } </code></pre> <p>segtree.h: #ifndef SEGTREE_H_ // NOLINT #define SEGTREE_H_</p> <pre><code>#include &lt;cassert&gt; #include &lt;functional&gt; #include &lt;vector&gt; template &lt;typename T&gt; class SegmentTree { private: std::vector&lt;T&gt; tree; int levels; int n; int el; std::function&lt;T(T, T)&gt; f; T query(int l, int r, int st, int fi) { if (l == r) return get(l); int mid = (st + fi + 1) / 2; if (r &lt; mid) { return query(l, r, st, mid - 1); } else if (l &gt;= mid) { return query(l, r, mid, fi); } else { T left = query(l, mid - 1, st, mid - 1); T right = query(mid, r, mid, fi); return f(left, right); } } public: SegmentTree(const std::vector&lt;T&gt;&amp; data, std::function&lt;T(T, T)&gt; f = std::plus &lt;T&gt;()) { this-&gt;f = f; this-&gt;n = data.size(); // build tree levels = 1, el = 1; while (el &lt; static_cast&lt;int&gt;(data.size())) { el &lt;&lt;= 1; ++levels; } tree.assign(2 * el, T()); for (size_t i = 0; i &lt; data.size(); ++i) tree[i + el - 1] = data[i]; for (int i = el - 2; i &gt;= 0; --i) tree[i] = f(tree[2 * i + 1], tree[2 * i + 2]); } SegmentTree(int n, T val = T(), std::function&lt;T(T, T)&gt; f = std::plus &lt;T&gt;()) : SegmentTree(std::vector&lt;T&gt;(n, val), f) { } T get(int l, int r) { return query(l, r, 0, n); } T get(int index) { return tree[el - 1 + index]; } void set(int index, T value) { int i = el - 1 + index; tree[i] = value; do { i = (i-1) / 2; tree[i] = f(tree[i*2 + 1], tree[i*2 + 2]); } while (i &gt; 0); } }; </code></pre> <p>Error information after <code>g++ main.cc</code>:</p> <pre><code>In file included from main.cc:9:0: segtree.h:22:3: error: ‘function’ in namespace ‘std’ does not name a type segtree.h:42:12: error: ‘std::function’ has not been declared segtree.h:42:20: error: expected ‘,’ or ‘...’ before ‘&lt;’ token segtree.h:60:12: error: ‘std::function’ has not been declared segtree.h:60:20: error: expected ‘,’ or ‘...’ before ‘&lt;’ token segtree.h:59:3: error: default argument missing for parameter 3 of ‘SegmentTree&lt;T&gt;::SegmentTree(int, T, int)’ segtree.h: In constructor ‘SegmentTree&lt;T&gt;::SegmentTree(const std::vector&lt;T&gt;&amp;, int)’: segtree.h:43:15: error: ‘f’ was not declared in this scope segtree.h: In constructor ‘SegmentTree&lt;T&gt;::SegmentTree(int, T, int)’: segtree.h:61:45: error: ‘f’ was not declared in this scope main.cc: In function ‘int main()’: main.cc:14:29: error: no matching function for call to ‘SegmentTree&lt;int&gt;::SegmentTree(const int&amp;, int, std::multiplies&lt;int&gt;)’ main.cc:14:29: note: candidates are: segtree.h:59:3: note: SegmentTree&lt;T&gt;::SegmentTree(int, T, int) [with T = int] segtree.h:59:3: note: no known conversion for argument 3 from ‘std::multiplies&lt;int&gt;’ to ‘int’ segtree.h:41:3: note: SegmentTree&lt;T&gt;::SegmentTree(const std::vector&lt;T&gt;&amp;, int) [with T = int] segtree.h:41:3: note: candidate expects 2 arguments, 3 provided segtree.h:16:7: note: SegmentTree&lt;int&gt;::SegmentTree(const SegmentTree&lt;int&gt;&amp;) segtree.h:16:7: note: candidate expects 1 argument, 3 provided In file included from main.cc:9:0: segtree.h: In member function ‘void SegmentTree&lt;T&gt;::set(int, T) [with T = int]’: main.cc:16:29: instantiated from here segtree.h:78:7: error: ‘f’ was not declared in this scope segtree.h: In member function ‘T SegmentTree&lt;T&gt;::query(int, int, int, int) [with T = int]’: segtree.h:66:28: instantiated from ‘T SegmentTree&lt;T&gt;::get(int, int) [with T = int]’ main.cc:20:35: instantiated from here segtree.h:36:27: error: ‘f’ was not declared in this scope </code></pre> <p>I got this piece of code from github, but I am not very familiar with c++. Can anyone help?</p>
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    1. COLooks like you accidentally pasted your .cc file twice instead of the header.
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    2. COAny chance we can see the *real* segtree.h?
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    3. COlooks like this one as he mentions on github: https://github.com/sochka/segtree/blob/master/segtree.h
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