When Are C Temporary Objects Destroyed?

Guaranteed Lifetime of Temporary Objects in C

In C , a temporary variable is created when an expression evaluates to a value that is not stored in a named variable. In the given code, a temporary StringBuffer object is created within the GetString() function call:

StringBuffer(mystring).Size(MAXLEN)

The question arises as to when the destructor for this temporary object will be called:

Lifetime of Temporary Objects:

C guarantees that a temporary object's lifetime extends until the end of the full-expression in which it is created. A full-expression is the outermost expression that is not part of any other expression. In this case, the full-expression is the entire GetString() function call:

GetString(StringBuffer(mystring).Size(MAXLEN), MAXLEN);

Destruction Timing:

Therefore, the destructor for the temporary StringBuffer object will be called after the GetString() function returns and the value is evaluated. This behavior is guaranteed by the C Standard in 12.2 "Temporary objects."

Significance for Expression Templates:

This lifetime guarantee is crucial for expression templates, which can hold references to temporary objects within expressions. For instance, the following expression template:

e = a + b * c / d

Can retain references to the temporary objects created by each operand because each temporary object's lifetime extends until the end of the entire expression.

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