Assignment operators
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| Operator | Operator name | Example | Description | Equivalent of |
|---|---|---|---|---|
| = | basic assignment | a = b | a becomes equal to b | N/A |
| += | addition assignment | a += b | a becomes equal to the addition of a and b | a = a + b |
| -= | subtraction assignment | a -= b | a becomes equal to the subtraction of b from a | a = a - b |
| *= | multiplication assignment | a *= b | a becomes equal to the product of a and b | a = a * b |
| /= | division assignment | a /= b | a becomes equal to the division of a by b | a = a / b |
| %= | modulo assignment | a %= b | a becomes equal to the remainder of a divided by b | a = a % b |
| &= | bitwise AND assignment | a &= b | a becomes equal to the bitwise AND of a and b | a = a & b |
| |= | bitwise OR assignment | a |= b | a becomes equal to the bitwise OR of a and b | a = a | b |
| ^= | bitwise XOR assignment | a ^= b | a becomes equal to the bitwise XOR of a and b | a = a ^ b |
| <<= | bitwise left shift assignment | a <<= b | a becomes equal to a left shifted by b | a = a << b |
| >>= | bitwise right shift assignment | a >>= b | a becomes equal to a right shifted by b | a = a >> b |
Simple assignment
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lhs = rhs
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Assignment performs MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 58 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE from the value of rhs to the type of lhs and then replaces the value in the object designated by lhs with the converted value of rhs.
Assignment also returns the same value as what was stored in lhs (so that expressions such as a = b = c are possible). The MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 57 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE of the assignment operator is non-lvalue (so that expressions such as (a=b)=c are invalid).
rhs and lhs must satisfy one of the following:
- both lhs and rhs have MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 55 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 57 MINUTES 54 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 57 MINUTES 53 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE type, or..
- rhs must be MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 52 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE to lhs, which implies
- both lhs and rhs have MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 50 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, in which case lhs may be MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 49 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE-qualified or MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 48 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(since 哋它亢11)
- both lhs and rhs have MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 47 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE to MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 45 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE (ignoring qualifiers) types, or one of the pointers is a pointer to void, and the MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 44 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE would not add qualifiers to the pointed-to type. lhs may be MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 43 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 57 MINUTES 42 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(since 哋它亢99)-qualified or MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 40 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(since 哋它亢11).
- lhs is a (possibly qualified or atomic(since 哋它亢11)) pointer and rhs is a null pointer constant such as MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 39 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE or a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 38 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE value(since 哋它亢23)
|
(since 哋它亢99) |
Notes
If rhs and lhs overlap in memory (e.g. they are members of the same union), the behavior is undefined unless the overlap is exact and the types are MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 33 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
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The side effect of updating lhs is MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 31 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE the value computations, but not the side effects of lhs and rhs themselves and the evaluations of the operands are, as usual, unsequenced relative to each other (so the expressions such as i=++i; are undefined)
Assignment strips extra range and precision from floating-point expressions (see MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 29 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE).
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#include <stdio.h> int main(void) { // integers int i = 1, j = 2, k = 3; // initialization, not assignment i = j = k; // values of i and j are now 3 // (i = j) = k; // Error: lvalue required MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 27 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d %d %d\n", i, j, k); // pointers const char c = 'A'; // initialization; not assignment const char *p = &c; // initialization; not assignment const char **cpp = &p; // initialization; not assignment // cpp = &p; // Error: char** is not convertible to const char** *cpp = &c; // OK, char* is convertible to const char* MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 25 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%c \n", **cpp); cpp = 0; // OK, null pointer constant is convertible to any pointer // arrays int arr1[2] = {1,2}, arr2[2] = {3, 4}; // arr1 = arr2; // Error: cannot assign to an array MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 24 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("arr1[0]=%d arr1[1]=%d arr2[0]=%d arr2[1]=%d\n", arr1[0], arr1[1], arr2[0], arr2[1]); struct { int arr[2]; } sam1 = { {5, 6} }, sam2 = { {7, 8} }; sam1 = sam2; // OK: can assign arrays wrapped in structs MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 23 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d %d \n", sam1.arr[0], sam1.arr[1]); }
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3 3 3 A arr1[0]=1 arr1[1]=2 arr2[0]=3 arr2[1]=4 7 8
Compound assignment
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| lhs op rhs | |||||||||
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| op | - | one of *=, /= %=, += -=, <<=, >>=, &=, ^=, |= |
| lhs, rhs | - | expressions with MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 18 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE (where lhs may be qualified or atomic), except when op is += or -=, which also accept pointer types with the same restrictions as + and - |
The expression lhs @= rhs is exactly the same as lhs = lhs @ ( rhs ), except that lhs is evaluated only once.
|
If lhs has MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 17 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE type, the operation behaves as a single atomic read-modify-write operation with memory order MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 16 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE. For integer atomic types, the compound assignment @= is equivalent to: T1* addr = &lhs; T2 val = rhs; T1 old = *addr; T1 new; do { new = old @ val } while (!MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 14 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(addr, &old, new); |
(since 哋它亢11) |
#include <stdio.h> int main(void) { int x = 10; int hundred = 100; int ten = 10; int fifty = 50; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 13 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d %d %d %d\n", x, hundred, ten, fifty); hundred *= x; ten /= x; fifty %= x; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 57 MINUTES 12 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d %d %d %d\n", x, hundred, ten, fifty); return 0; }
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10 100 10 50 10 1000 1 0
References
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.5.16 Assignment operators (p: 72-73)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.5.16 Assignment operators (p: 101-104)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.5.16 Assignment operators (p: 91-93)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 3.3.16 Assignment operators