Member access operators
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Subscript
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pointer-expression [ integer-expression ]
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integer-expression [ pointer-expression ]
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| pointer-expression | - | an MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 28 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE of type pointer to complete object |
| integer-expression | - | an MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 27 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE of integer type |
The subscript operator expression is an MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 26 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE whose type is the type of the object pointed to by pointer-expression.
By definition, the subscript operator E1[E2] is exactly identical to *((E1)+(E2)). If pointer-expression is an array expression, it undergoes MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 25 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE and becomes a pointer to the first element of the array.
Due to the definition of the MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 23 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, the result is the element of the array with the index equal to the result of integer-expression (or, if pointer-expression was pointing at ith element of some array, the index of the result is i plus the result of integer-expression)
Note: see MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 22 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE for the details on multidimensional arrays.
#include <stdio.h> int main(void) { int a[3] = {1,2,3}; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 21 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d %d\n", a[2], // n == 3 2[a]); // same, n == 3 a[2] = 7; // subscripts are lvalues int n[2][3] = {{1,2,3},{4,5,6}}; int (*p)[3] = &n[1]; // elements of n are arrays MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 20 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d %d %d\n", (*p)[0], p[0][1], p[0][2]); // access n[1][] via p int x = n[1][2]; // applying [] again to the array n[1] MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 19 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d\n", x); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 17 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%c %c\n", "abc"[2], 2["abc"]); // string literals are arrays too }
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3 3 4 5 6 6 c c
Dereference
The dereference or indirection expression has the form
* pointer-expression
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If pointer-expression is a pointer to function, the result of the dereference operator is a function designator for that function.
If pointer-expression is a pointer to object, the result is an MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 12 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE that designates the pointed-to object.
Dereferencing a null pointer, a pointer to an object outside of its lifetime (a dangling pointer), a misaligned pointer, or a pointer with indeterminate value is undefined behavior, except when the dereference operator is nullified by applying the address-of operator to its result, as in &*E.
#include <stdio.h> int main(void) { int n = 1; int* p = &n; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 11 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("*p = %d\n", *p); // the value of *p is what's stored in n *p = 7; // *p is lvalue MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 10 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("*p = %d\n", *p); }
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*p = 1 *p = 7
Address of
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& function
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& lvalue-expression
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& * expression
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& expression [ expression ]
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(4) | ||||||||
& and * cancel each other, neither one is evaluated& and the * that is implied in [] cancel each other, only the addition implied in [] is evaluated.MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 06 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
The address-of operator produces the MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 54 MINUTES 01 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE address of its operand, suitable for initializing a pointer to the type of the operand. If the operand is a function designator (1), the result is a pointer to function. If the operand is an object (2), the result is a pointer to object.
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int f(char c) { return c;} int main(void) { int n = 1; int *p = &n; // address of object n int (*fp)(char) = &f; // address of function f int a[3] = {1,2,3}; int *beg=a, *end=&a[3]; // same as end = a+3 }
Member access
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expression . member-name
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The member access expression designates the named member of the MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 51 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 53 MINUTES 50 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE designated by its left operand. It has the same MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 49 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE as its left operand.
If the left operand is MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 47 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 53 MINUTES 46 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE qualified, the result is also qualified. If the left operand is MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 45 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, the behavior is undefined.
Note: besides identifiers that name objects of struct or union type, the following expressions may have struct or union types: MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 44 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 53 MINUTES 42 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 53 MINUTES 41 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 53 MINUTES 40 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 53 MINUTES 39 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
#include <stdio.h> struct s {int x;}; struct s f(void) { return (struct s){1}; } int main(void) { struct s s; s.x = 1; // ok, changes the member of s int n = f().x; // f() is an expression of type struct s // f().x = 1; // Error: this member access expression is not an lvalue const struct s sc; // sc.x = 3; // Error: sc.x is const, can't be assigned union { int x; double d; } u = {1}; u.d = 0.1; // changes the active member of the union }
Member access through pointer
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expression -> member-name
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The member access through pointer expression designates the named member of the MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 30 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 53 MINUTES 29 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE type pointed to by its left operand. Its value category is always MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 28 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
If the type pointed to by the left operand is MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 26 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 53 MINUTES 25 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE qualified, the result is also qualified. If the type pointed to by the left operand is MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 24 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, the behavior is undefined.
#include <stdio.h> struct s {int x;}; int main(void) { struct s s={1}, *p = &s; p->x = 7; // changes the value of s.x through the pointer MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 53 MINUTES 23 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d\n", p->x); // prints 7 }
Defect reports
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| DR | Applied to | Behavior as published | Correct behavior |
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made cancellable |
References
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.5.2.1 Array subscripting (p: 57-58)
- 6.5.2.3 Structure and union members (p: 58-59)
- 6.5.3.2 Address and indirection operators (p: 59-61)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.5.2.1 Array subscripting (p: 80)
- 6.5.2.3 Structure and union members (p: 82-84)
- 6.5.3.2 Address and indirection operators (p: 88-89)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.5.2.1 Array subscripting (p: 70)
- 6.5.2.3 Structure and union members (p: 72-74)
- 6.5.3.2 Address and indirection operators (p: 78-79)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 3.3.2.1 Array subscripting
- 3.3.2.3 Structure and union members
- 3.3.3.2 Address and indirection operators