Sequence Point and Evaluation Order( Preincrement)
- by Josh
There was a debate today among some of my colleagues and I wanted to clarify it. It is about the evaluation order and the sequence point in an expression. It is clearly stated in the standard that C/C++ does not have a left-to-right evaluation in an expression unlike languages like Java which is guaranteed to have a sequencial left-to-right order. So, in the below expression, the evaluation of the leftmost operand(B) in the binary operation is sequenced before the evaluation of the rightmost operand(C):
A = B B_OP C
The following expression according, to CPPReference under the subsection Sequenced-before rules(Undefined Behaviour) and Bjarne's TCPPL 3rd ed, is an UB
x = x++ + 1;
It could be interpreted as the compilers like BUT the expression below is said to be clearly a well defined behaviour in C++11
x = ++x + 1;
So, if the above expression is well defined, what is the "fate" of this?
array[x] = ++x;
It seems the evaluation of a post-increment and post-decrement is not defined but the pre-increment and the pre-decrement is defined.
NOTE: This is not used in a real-life code. Clang 3.4 and GCC 4.8 clearly warns about both the pre- and post-increment sequence point.
