What's the deal with "sequence points"?, C++ FAQ

C++ FAQ / Section 39 / FAQ 39.16

Section 39:

39.1	How do I convert a value (a number, for example) to a `std::string`?
39.2	How do I convert a `std::string` to a number?
39.3	Can I templatize the above functions so they work with other types?
39.4	What should be done with macros that contain `if`?
39.5	What should be done with macros that have multiple lines?
39.6	What should be done with macros that need to paste two tokens together? Updated!
39.7	Why can't the compiler find my header file in `#include "c:\test.h"` ?
39.8	What are the C++ scoping rules for `for` loops?
39.9	Why can't I overload a function by its return type?
39.10	What is "persistence"? What is a "persistent object"?
39.11	How can I create two classes that both know about each other?
39.12	What special considerations are needed when forward declarations are used with member objects?
39.13	What special considerations are needed when forward declarations are used with inline functions?
39.14	Why can't I put a forward-declared class in a `std::vector<>`?
39.15	Why do some people think `x = ++y + y++` is bad?
39.16	What's the deal with "sequence points"?

[39.16] What's the deal with "sequence points"?

The C++ standard says (1.9p7),

At certain specified points in the execution sequence called sequence points, all side effects of previous evaluations shall be complete and no side effects of subsequent evaluations shall have taken place.

For example, if an expression contains the subexpression y++, then the variable y will be incremented by the next sequence point. Furthermore if the expression just after the sequence point contains the subexpression ++z, then z will not have yet been incremented at the moment the sequence point is reached.

The "certain specified points" that are called sequence points are (section and paragraph numbers are from the standard):

the semicolon (1.9p16)
the non-overloaded comma-operator (1.9p18)
the non-overloaded || operator (1.9p18)
the non-overloaded && operator (1.9p18)
the ternary ?: operator (1.9p18)
after evaluation of all a function's parameters but before the first expression within the function is executed (1.9p17)
after a function's returned object has been copied back to the caller, but before the code just after the call has yet been evaluated (1.9p17)
after the initialization of each base and member (12.6.2p3)