Evaluation of an expression may produce side effects. At specific points in the execution sequence called sequence points, all side effects of previous evaluations have completed, and no side effects of subsequent evaluations have yet taken place.
| Wiki Markup |
|---|
The following sequence points are defined by C99 \[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\]: |
- the call to a function, after the arguments have been evaluated
- the end of the first operand of the following operators: && (logical AND); || (logical OR); ? (conditional); , (comma, but see the note below)
- the end of a full declarator
- the end of a full expression: an initializer; the expression in an expression statement; the controlling expression of a selection statement (if or switch); the controlling expression of a while or do statement; each of the expressions of a for statement; the expression in a return statement
- immediately before a library function returns
- after the actions associated with each formatted input/output function conversion specifier
- immediately before and immediately after each call to a comparison function, and also between any call to a comparison function and any movement of the objects passed as arguments to that call
Note that not all instances of a comma in C code denote a usage of the comma operator. For example, the comma between arguments in a function call is NOT the comma operator.
According to C99:
Between the previous and next sequence point an object can only have its stored value modified once by the evaluation of an expression. Additionally, the prior value can be read only to determine the value to be stored.
...