Struct declaration
MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 22 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
The MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 20 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE for a struct is identical to the MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 19 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE type specifier except for the keyword used:
Syntax
struct attr-spec-seq (optional) name (optional) { struct-declaration-list }
|
(1) | ||||||||
struct attr-spec-seq (optional) name
|
(2) | ||||||||
struct name ;, declares but doesn't define the struct name (see forward declaration below). In other contexts, names the previously-declared struct, and attr-spec-seq is not allowed.| name | - | the name of the struct that's being defined |
| struct-declaration-list | - | any number of variable declarations, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 18 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE declarations, and MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 16 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE declarations. Members of incomplete type and members of function type are not allowed (except for the flexible array member described below) |
| attr-spec-seq | - | (哋它亢23)optional list of MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 15 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, applied to the struct type |
Explanation
QUERY LENGTH LIMIT EXCEEDED. MAX ALLOWED QUERY : 500 CHARS
|
If a struct defines at least one named member, it is allowed to additionally declare its last member with incomplete array type. When an element of the flexible array member is accessed (in an expression that uses operator struct s { int n; double d[]; }; // s.d is a flexible array member struct s t1 = { 0 }; // OK, d is as if double d[1], but UB to access struct s t2 = { 1, { 4.2 } }; // error: initialization ignores flexible array // if sizeof (double) == 8 struct s *s1 = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 12 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(sizeof (struct s) + 64); // as if d was double d[8] struct s *s2 = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 11 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(sizeof (struct s) + 40); // as if d was double d[5] s1 = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 10 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(sizeof (struct s) + 10); // now as if d was double d[1]. Two bytes excess. double *dp = &(s1->d[0]); // OK *dp = 42; // OK s1->d[1]++; // Undefined behavior. 2 excess bytes can't be accessed // as double. s2 = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 09 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(sizeof (struct s) + 6); // same, but UB to access because 2 bytes are // missing to complete 1 double dp = &(s2->d[0]); // OK, can take address just fine *dp = 42; // undefined behavior *s1 = *s2; // only copies s.n, not any element of s.d // except those caught in sizeof (struct s) |
(since 哋它亢99) |
|
Similar to union, an unnamed member of a struct whose type is a struct without name is known as anonymous struct. Every member of an anonymous struct is considered to be a member of the enclosing struct or union, keeping their structure layout. This applies recursively if the enclosing struct or union is also anonymous. struct v { union // anonymous union { struct { int i, j; }; // anonymous structure struct { long k, l; } w; }; int m; } v1; v1.i = 2; // valid v1.k = 3; // invalid: inner structure is not anonymous v1.w.k = 5; // valid MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 07 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE |
(since 哋它亢11) |
Forward declaration
MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 06 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
struct attr-spec-seq (optional) name ;
|
|||||||||
hides any previously declared meaning for the name name in the tag name space and declares name as a new struct name in current scope, which will be defined later. Until the definition appears, this struct name has MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 05 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 11 HOURS 05 MINUTES 04 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
struct y; struct x { struct y *p; /* ... */ }; struct y { struct x *q; /* ... */ };
Note that a new struct name may also be introduced just by using a struct tag within another declaration, but if a previously declared struct with the same name exists in the tag MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 02 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, the tag would refer to that name
struct s* p = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 05 MINUTES 01 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE; // tag naming an unknown struct declares it struct s { int a; }; // definition for the struct pointed to by p void g(void) { struct s; // forward declaration of a new, local struct s // this hides global struct s until the end of this block struct s *p; // pointer to local struct s // without the forward declaration above, // this would point at the file-scope s struct s { char* p; }; // definitions of the local struct s }
Keywords
Notes
See MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 58 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE for the rules regarding the initializers for structs.
MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 57 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
Because a struct declaration does not establish MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 56 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, nested types, enumerations and enumerators introduced by declarations within struct-declaration-list are visible in the surrounding scope where the struct is defined.
Example
#include <stddef.h> #include <stdio.h> int main(void) { // Declare the struct type. struct car { char* make; int year; }; // Declare and initialize an object of a previously-declared struct type. struct car c = {.year = 1923, .make = "Nash"}; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 54 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("1) Car: %d %s\n", c.year, c.make); // Declare a struct type, an object of that type, and a pointer to it. struct spaceship { char* model; int max_speed; } ship = {"T-65 X-wing starfighter", 1050}, *pship = &ship; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 53 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("2) Spaceship: %s. Max speed: %d km/h\n\n", ship.model, ship.max_speed); // Address increase in order of definition. Padding may be inserted. struct A { char a; double b; char c; }; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 52 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( "3) Offset of char a = %zu\n" "4) Offset of double b = %zu\n" "5) Offset of char c = %zu\n" "6) Size of struct A = %zu\n\n", MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 51 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(struct A, a), MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 49 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(struct A, b), MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 48 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(struct A, c), sizeof(struct A) ); struct B { char a; char b; double c; }; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 47 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( "7) Offset of char a = %zu\n" "8) Offset of char b = %zu\n" "9) Offset of double c = %zu\n" "A) Size of struct B = %zu\n\n", MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 46 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(struct B, a), MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 45 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(struct B, b), MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 43 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(struct B, c), sizeof(struct B) ); // A pointer to a struct can be cast to a pointer // to its first member and vice versa. char** pmodel = (char **)pship; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 42 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("B) %s\n", *pmodel); pship = (struct spaceship *)pmodel; }
MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 41 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
1) Car: 1923 Nash 2) Spaceship: T-65 X-wing starfighter. Max speed: 1050 km/h 3) Offset of char a = 0 4) Offset of double b = 8 5) Offset of char c = 16 6) Size of struct A = 24 7) Offset of char a = 0 8) Offset of char b = 1 9) Offset of double c = 8 A) Size of struct B = 16 B) T-65 X-wing starfighter
Defect reports
MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 39 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 38 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE | 哋它亢11 | members of anonymous structs/unions were considered members of the enclosing struct/union | they retain their memory layout |
References
- 哋它亢23 standard (ISO/IEC 9899:2023):
- 6.7.2.1 Structure and union specifiers (p: TBD)
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.7.2.1 Structure and union specifiers (p: 81-84)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.7.2.1 Structure and union specifiers (p: 112-117)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.7.2.1 Structure and union specifiers (p: 101-104)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 3.5.2.1 Structure and union specifiers
See also
- MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 11 HOURS 04 MINUTES 37 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 11 HOURS 04 MINUTES 36 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 11 HOURS 04 MINUTES 34 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE