QUESTION 17 · Scope and Lifetime
Scope tells where a name is visible; lifetime tells when its object exists during execution.
QUESTION 18 · Scope and Lifetime
Scope, lifetime and linkage answer three different questions about a declaration and its associated object.
A name declared inside a block generally has block scope. Outside that scope, the same spelling cannot be used to reach that declaration. Scope is a source-code rule about names, rather than a count of seconds or function calls.
An ordinary automatic local object is associated with a particular execution of its block. A static-duration object exists throughout program execution. A function call can end the lifetime of an ordinary automatic local object while a local static object continues to exist. Allocated objects have a different lifetime managed through memory allocation, covered in Unit V.
External linkage can connect declarations across translation units. Internal linkage connects declarations within one translation unit. A typical local variable has no linkage. Linkage is not the same as visibility: a file-scope static object has internal linkage, while a block-local static object has no linkage.
In void count(void) { static int total = 0; ++total; }, the name total has block scope. Its object has static storage duration, so the value can remain after count returns. A later call uses the same object. Scope is local, but the lifetime is not limited to one call.
Do not return a pointer to an ordinary local object that stops existing when the call ends. Do not assume that a local name always describes temporary storage. State scope, storage duration and linkage separately when comparing storage classes.
Related questions in the storage classes category from the supplied papers. The marks below are the printed allocations, including any combined subquestion.
If a variable has auto storage class by default, why was the auto keyword introduced in C? Explain.
Paper P01 · page 1List and explain storage classes in C.
Paper P04 · page 1