Why did the range based for loop specification change in C++17How to use range-based for() loop with std::map?C++11 reverse range-based for-loopWhy are elementwise additions much faster in separate loops than in a combined loop?Why does changing 0.1f to 0 slow down performance by 10x?Why is my program slow when looping over exactly 8192 elements?How the new range-based for loop in C++17 helps Ranges TS?Moving in range-based loop in generic C++ code?range based for used for primitive typeRange based for in C++17 for custom container or general classes with different begin/end types
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Why did the range based for loop specification change in C++17
How to use range-based for() loop with std::map?C++11 reverse range-based for-loopWhy are elementwise additions much faster in separate loops than in a combined loop?Why does changing 0.1f to 0 slow down performance by 10x?Why is my program slow when looping over exactly 8192 elements?How the new range-based for loop in C++17 helps Ranges TS?Moving in range-based loop in generic C++ code?range based for used for primitive typeRange based for in C++17 for custom container or general classes with different begin/end types
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty
margin-bottom:0;
I was looking over some ugly code(that was modifying the underlying sequence while iterating), and to explore the definition of range based for loop I went to cppreference.
There I noticed something strange:
range based for loop changed in C++17, but I do not see the reason for change, and code looks the same to me(just "refactored").
So old one was:
auto && __range = range_expression ;
for (auto __begin = begin_expr, __end = end_expr; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
New one is
auto && __range = range_expression ;
auto __begin = begin_expr ;
auto __end = end_expr ;
for ( ; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
My question is: why was this change made, and does it make any legal C++14 programs UB in C++17.
c++ for-loop language-lawyer c++17
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
add a comment
|
I was looking over some ugly code(that was modifying the underlying sequence while iterating), and to explore the definition of range based for loop I went to cppreference.
There I noticed something strange:
range based for loop changed in C++17, but I do not see the reason for change, and code looks the same to me(just "refactored").
So old one was:
auto && __range = range_expression ;
for (auto __begin = begin_expr, __end = end_expr; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
New one is
auto && __range = range_expression ;
auto __begin = begin_expr ;
auto __end = end_expr ;
for ( ; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
My question is: why was this change made, and does it make any legal C++14 programs UB in C++17.
c++ for-loop language-lawyer c++17
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
add a comment
|
I was looking over some ugly code(that was modifying the underlying sequence while iterating), and to explore the definition of range based for loop I went to cppreference.
There I noticed something strange:
range based for loop changed in C++17, but I do not see the reason for change, and code looks the same to me(just "refactored").
So old one was:
auto && __range = range_expression ;
for (auto __begin = begin_expr, __end = end_expr; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
New one is
auto && __range = range_expression ;
auto __begin = begin_expr ;
auto __end = end_expr ;
for ( ; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
My question is: why was this change made, and does it make any legal C++14 programs UB in C++17.
c++ for-loop language-lawyer c++17
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
I was looking over some ugly code(that was modifying the underlying sequence while iterating), and to explore the definition of range based for loop I went to cppreference.
There I noticed something strange:
range based for loop changed in C++17, but I do not see the reason for change, and code looks the same to me(just "refactored").
So old one was:
auto && __range = range_expression ;
for (auto __begin = begin_expr, __end = end_expr; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
New one is
auto && __range = range_expression ;
auto __begin = begin_expr ;
auto __end = end_expr ;
for ( ; __begin != __end; ++__begin)
range_declaration = *__begin;
loop_statement
My question is: why was this change made, and does it make any legal C++14 programs UB in C++17.
c++ for-loop language-lawyer c++17
c++ for-loop language-lawyer c++17
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
edited 7 hours ago
Barry
201k22 gold badges379 silver badges673 bronze badges
201k22 gold badges379 silver badges673 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
asked 9 hours ago
NoSenseEtAlNoSenseEtAl
8,20218 gold badges79 silver badges197 bronze badges
8,20218 gold badges79 silver badges197 bronze badges
add a comment
|
add a comment
|
2 Answers
2
active
oldest
votes
Using
auto __begin = begin_expr, __end = end_expr;
requires both begin_expr and end_expr to return the same type. This means you cannot have a sentinel iterator type that is different from the beginning type. Using
auto __begin = begin_expr ;
auto __end = end_expr ;
fixes that issue while proving full backwards compatibility with C++14.
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
add a comment
|
It is explained later in the "notes":
As of C++17, the types of the begin_expr and the end_expr do not have to be the same ...
and you can't have that with:
auto __begin = begin_expr, __end = end_expr;
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
add a comment
|
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Using
auto __begin = begin_expr, __end = end_expr;
requires both begin_expr and end_expr to return the same type. This means you cannot have a sentinel iterator type that is different from the beginning type. Using
auto __begin = begin_expr ;
auto __end = end_expr ;
fixes that issue while proving full backwards compatibility with C++14.
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
add a comment
|
Using
auto __begin = begin_expr, __end = end_expr;
requires both begin_expr and end_expr to return the same type. This means you cannot have a sentinel iterator type that is different from the beginning type. Using
auto __begin = begin_expr ;
auto __end = end_expr ;
fixes that issue while proving full backwards compatibility with C++14.
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
add a comment
|
Using
auto __begin = begin_expr, __end = end_expr;
requires both begin_expr and end_expr to return the same type. This means you cannot have a sentinel iterator type that is different from the beginning type. Using
auto __begin = begin_expr ;
auto __end = end_expr ;
fixes that issue while proving full backwards compatibility with C++14.
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
Using
auto __begin = begin_expr, __end = end_expr;
requires both begin_expr and end_expr to return the same type. This means you cannot have a sentinel iterator type that is different from the beginning type. Using
auto __begin = begin_expr ;
auto __end = end_expr ;
fixes that issue while proving full backwards compatibility with C++14.
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
edited 8 hours ago
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
answered 9 hours ago
NathanOliverNathanOliver
117k19 gold badges187 silver badges265 bronze badges
117k19 gold badges187 silver badges265 bronze badges
add a comment
|
add a comment
|
It is explained later in the "notes":
As of C++17, the types of the begin_expr and the end_expr do not have to be the same ...
and you can't have that with:
auto __begin = begin_expr, __end = end_expr;
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
add a comment
|
It is explained later in the "notes":
As of C++17, the types of the begin_expr and the end_expr do not have to be the same ...
and you can't have that with:
auto __begin = begin_expr, __end = end_expr;
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
add a comment
|
It is explained later in the "notes":
As of C++17, the types of the begin_expr and the end_expr do not have to be the same ...
and you can't have that with:
auto __begin = begin_expr, __end = end_expr;
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
It is explained later in the "notes":
As of C++17, the types of the begin_expr and the end_expr do not have to be the same ...
and you can't have that with:
auto __begin = begin_expr, __end = end_expr;
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
answered 9 hours ago
danadamdanadam
1,63712 silver badges12 bronze badges
1,63712 silver badges12 bronze badges
add a comment
|
add a comment
|
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