Scope
Each MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 58 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE that appears in a C program is visible (that is, may be used) only in some possibly discontiguous portion of the source code called its scope.
Within a scope, an identifier may designate more than one entity only if the entities are in different MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 57 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
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- block scope
- file scope
- function scope
- function prototype scope
Nested scopes
If two different entities named by the same identifier are in scope at the same time, and they belong to the same MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 54 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, the scopes are nested (no other form of scope overlap is allowed), and the declaration that appears in the inner scope hides the declaration that appears in the outer scope:
// The name space here is ordinary identifiers. int a; // file scope of name a begins here void f(void) { int a = 1; // the block scope of the name a begins here; hides file-scope a { int a = 2; // the scope of the inner a begins here, outer a is hidden MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 53 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d\n", a); // inner a is in scope, prints 2 } // the block scope of the inner a ends here MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 51 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d\n", a); // the outer a is in scope, prints 1 } // the scope of the outer a ends here void g(int a); // name a has function prototype scope; hides file-scope a
Block scope
The scope of any identifier declared inside a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 50 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, including function bodies, or in any expression, declaration, or statement appearing in MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 49 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 48 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 47 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 45 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, or MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 44 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE statement(since 哋它亢99), or within the parameter list of a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 42 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE begins at the point of declaration and ends at the end of the block or statement in which it was declared.
void f(int n) // scope of the function parameter 'n' begins { // the body of the function begins ++n; // 'n' is in scope and refers to the function parameter // int n = 2; // error: cannot redeclare identifier in the same scope for(int n = 0; n<10; ++n) { // scope of loop-local 'n' begins MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 41 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d\n", n); // prints 0 1 2 3 4 5 6 7 8 9 } // scope of the loop-local 'n' ends // the function parameter 'n' is back in scope MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 40 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d\n", n); // prints the value of the parameter } // scope of function parameter 'n' ends int a = n; // Error: name 'n' is not in scope
|
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(since 哋它亢99) |
Block-scope variables have MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 38 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE and MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 36 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE by default. Note that storage duration for non-VLA local variables begins when the block is entered, but until the declaration is seen, the variable is not in scope and cannot be accessed.
File scope
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int i; // scope of i begins static int g(int a) { return a; } // scope of g begins (note, "a" has block scope) int main(void) { i = g(2); // i and g are in scope }
File-scope identifiers have MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 34 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE and MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 32 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE by default.
Function scope
A MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 31 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE declared inside a function is in scope everywhere in that function, in all nested blocks, before and after its own declaration. Note: a label is declared implicitly, by using an otherwise unused identifier before the colon character before any statement.
void f() { { goto label; // label in scope even though declared later label:; } goto label; // label ignores block scope } void g() { goto label; // error: label not in scope in g() }
Function prototype scope
The scope of a name introduced in the parameter list of a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 30 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE that is not a definition ends at the end of the function MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 29 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
int f(int n, int a[n]); // n is in scope and refers to the first parameter
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void f ( // function name 'f' is at file scope long double f, // the identifier 'f' is now in scope, file-scope 'f' is hidden char (**a)[10 * sizeof f] // 'f' refers to the first parameter, which is in scope ); enum{ n = 3 }; int (*(*g)(int n))[n]; // the scope of the function parameter 'n' // ends at the end of its function declarator // in the array declarator, global n is in scope // (this declares a pointer to function returning a pointer to an array of 3 int)
Point of declaration
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struct Node { struct Node* next; // Node is in scope and refers to this struct };
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enum { x = 12 }; { enum { x = x + 1, // new x is not in scope until the comma, x is initialized to 13 y = x + 1 // the new enumerator x is now in scope, y is initialized to 14 }; }
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int x = 2; // scope of the first 'x' begins { int x[x]; // scope of the newly declared x begins after the declarator (x[x]). // Within the declarator, the outer 'x' is still in scope. // This declares a VLA array of 2 int. }
unsigned char x = 32; // scope of the outer 'x' begins { unsigned char x = x; // scope of the inner 'x' begins before the initializer (= x) // this does not initialize the inner 'x' with the value 32, // this initializes the inner 'x' with its own, indeterminate, value } unsigned long factorial(unsigned long n) // declarator ends, 'factorial' is in scope from this point { return n<2 ? 1 : n*factorial(n-1); // recursive call }
As a special case, the scope of a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 22 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE that is not a declaration of an identifier is considered to begin just after the place within the type name where the identifier would appear were it not omitted.
Notes
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Local variables within a loop body can hide variables declared in the init clause of a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 20 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE loop in C (their scope is nested), but cannot do that in 哋它亢++.
Unlike 哋它亢++, C has no struct scope: names declared within a struct/union/enum declaration are in the same scope as the struct declaration (except that data members are in their own MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 59 MINUTES 18 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE):
struct foo { struct baz {}; enum color {RED, BLUE}; }; struct baz b; // baz is in scope enum color x = RED; // color and RED are in scope
References
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.2.1 Scopes of identifiers (p: 28-29)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.2.1 Scopes of identifiers (p: 35-36)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.2.1 Scopes of identifiers (p: 29-30)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 3.1.2.1 Scopes of identifiers