{"id":715,"date":"2017-11-24T23:20:11","date_gmt":"2017-11-25T07:20:11","guid":{"rendered":"http:\/\/wonghoi.humgar.com\/blog\/?p=715"},"modified":"2017-11-28T04:42:41","modified_gmt":"2017-11-28T12:42:41","slug":"begin-and-end-is-defined-for-arrays-in-c11-and-above","status":"publish","type":"post","link":"https:\/\/wonghoi.humgar.com\/blog\/2017\/11\/24\/begin-and-end-is-defined-for-arrays-in-c11-and-above\/","title":{"rendered":"begin() and end() is defined for arrays in C++11 and above"},"content":{"rendered":"

I was a little confused the first time I saw range-based for-loop in C++11 on “Tour of C++” that it works right out of the box for both recognized<\/em> array<\/a> and STL containers and yet the text says it requires begin() and end() to be defined for the object for range-based for-loop to run.<\/p>\n

I later learned that despite typical STL usage example writes v.begin(), v.end()<\/code>, the most bulletproof way is to write begin(v), end(v)<\/code> instead (Herb Sutter recommends it). Then I started to suspect that C++11 must have defined free-form (non-member) begin(), end()<\/code> functions that takes in arbitrary recognized<\/em> arrays. I pulled up my code editor and ran this:<\/p>\n

#include <iostream>\r\nint main()\r\n{\r\n    int v[4]={1,2,3,4};\r\n    std::cout << *(std::crend(v)-1) << std::endl;\r\n\r\n    return 0;\r\n}\r\n<\/pre>\n
It compiled and ran uneventfully, printing ‘1’ as expected (I’m using crend()<\/code>, to see if they implemented the more obscure ones). It makes more sense now why range-based for-loop works for arbitrary recognized<\/em> arrays without making an exception to the begin(), end()<\/code> requirement.<\/p>\n
To confirm that it is the case (since “Tour of C++” didn’t say anything about why arbitrary array works for range-based for loop), I looked up the STL source code from libc++ in LLVM, namely <iterator<\/a>>, and saw this:<\/p>\n
template\u00a0<class\u00a0T,\u00a0size_t\u00a0N>\u00a0constexpr\u00a0T*\u00a0begin(T\u00a0(&array)[N]);<\/pre>\n
Bingo! There’s a mechanism to do so. But before I close, Stephan T. Lavavej (Mr. STL) mentioned<\/a> that the template quoted above is no longer required (by the standard) to implement range-based for-loop in C++11.<\/p>\n
Now the conclusion becomes that\u00a0begin(), end()<\/code>\u00a0that takes in recognized<\/em> arrays exist (which completes the logic behind range-based for-loop), but the range-based for loop can (and typically will) handle recognized<\/em> arrays without these templated functions defined.<\/p>\n
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I was a little confused the first time I saw range-based for-loop in C++11 on “Tour of C++” that it works right out of the box for both recognized array and STL containers and yet the text says it requires … Continue reading →<\/span><\/a><\/p>\n
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