Comparison operators
Comparison operators are binary operators that test a condition and return 1 if that condition is logically true and 0 if that condition is false.
| Operator | Operator name | Example | Description |
|---|---|---|---|
| == | equal to | a == b | a is equal to b |
| != | not equal to | a != b | a is not equal to b |
| < | less than | a < b | a is less than b |
| > | greater than | a > b | a is greater than b |
| <= | less than or equal to | a <= b | a is less than or equal to b |
| >= | greater than or equal to | a >= b | a is greater than or equal to b |
Relational operators
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lhs < rhs
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(1) | ||||||||
lhs > rhs
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(2) | ||||||||
lhs <= rhs
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(3) | ||||||||
lhs >= rhs
|
(4) | ||||||||
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| lhs, rhs | - | expressions that both have real type or both have pointer to object type |
The type of any relational operator expression is int, and its value (which is not an lvalue) is 1 when the specified relationship holds true and 0 when the specified relationship does not hold.
If lhs and rhs are expressions of any MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 45 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, then
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- the values of the operands after conversion are compared in the usual mathematical sense (except that positive and negative zeroes compare equal and any comparison involving a NaN value returns zero)
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If lhs and rhs are expressions of pointer type, they must be both pointers to objects of MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 41 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, except that qualifications of the pointed-to objects are ignored.
- a pointer to an object that is not an element of an array is treated as if it were pointing to an element of an array with one element
- if two pointers point to the same object, or both point one past the end of the same array, they compare equal
- if two pointers point to different elements of the same array, the one pointing at the element with the larger index compares greater.
- if one pointer points to the element of an array and the other pointer points one past the end of the same array, the one-past-the-end pointer compares greater
- if the two pointers point to members of the same MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 40 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, the pointer to the member declared later in the struct definition compares greater than then pointer to the member declared earlier.
- pointers to members of the same union compare equal
- all other pointer comparisons invoke undefined behavior
#include <assert.h> int main(void) { MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 39 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(1 < 2); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 38 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(2+2 <= 4.0); // int converts to double, two 4.0's compare equal struct { int x,y; } s; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 37 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(&s.x < &s.y); // struct members compare in order of declaration double d = 0.0/0.0; // NaN MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 35 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( !(d < d) ); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 34 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( !(d > d) ); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 33 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( !(d <= d) ); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 31 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( !(d >= d) ); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 30 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( !(d == d) ); float f = 0.1; // f = 0.100000001490116119384765625 double g = 0.1; // g = 0.1000000000000000055511151231257827021181583404541015625 MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 29 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(f > g); // different values }
Equality operators
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lhs == rhs
|
(1) | ||||||||
lhs != rhs
|
(2) | ||||||||
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The type of any equality operator expression is int, and its value (which is not an lvalue) is 1 when the specified relationship holds true and 0 when the specified relationship does not hold.
- if both operands have arithmetic types, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 19 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE are performed and the resulting values are compared in the usual mathematical sense (except that positive and negative zeroes compare equal and any comparison involving a NaN value, including equality with itself, returns zero). In particular, values of complex type are equal if their real parts compare equal and their imaginary parts compare equal.
|
(since 哋它亢23) |
- if one operand is a pointer and the other is a null pointer constant, the null pointer constant is first MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 15 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE to the type of the pointer (which gives a null pointer value), and the two pointers are compared as described below
- if one operand is a pointer and the other is a pointer to void, the non-void pointer is MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 14 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE to the pointer to void and the two pointers are compared as described below
- two pointers compare equal if any of the following is true:
- they are both null pointer values of their type
- they are both pointers to the same object or function
- one pointer is to a struct/union/array object and the other is to its first member/any member/first element
- they are both pointing one past the last element of the same array
- one is one past the end of an array, and the other is at the start of a different array (of the same type) that follows the first in a larger array or in a struct with no padding
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Notes
Objects of struct type do not compare equal automatically, and comparing them with MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 12 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE is not reliable because the padding bytes may have any values.
Because pointer comparison works with pointers to void, the macro MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 11 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE may be defined as (void*)0 in C, although that would be invalid in 哋它亢++ where void pointers do not implicitly convert to typed pointers
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#include <assert.h> int main(void) { MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 09 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(2+2 == 4.0); // int converts to double, two 4.0's compare equal int n[2][3] = {1,2,3,4,5,6}; int* p1 = &n[0][2]; // last element in the first row int* p2 = &n[1][0]; // start of second row MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 08 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(p1+1 == p2); // compare equal double d = 0.0/0.0; // NaN MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 07 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE( d != d ); // NaN does not equal itself float f = 0.1; // f = 0.100000001490116119384765625 double g = 0.1; // g = 0.1000000000000000055511151231257827021181583404541015625 MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 09 HOURS 46 MINUTES 05 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(f != g); // different values }
References
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.5.8 Relational operators (p: 68-69)
- 6.5.9 Equality operators (p: 69-70)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.5.8 Relational operators (p: 95-96)
- 6.5.9 Equality operators (p: 96-97)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.5.8 Relational operators (p: 85-86)
- 6.5.9 Equality operators (p: 86-87)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 3.3.8 Relational operators
- 3.3.9 Equality operators
See also
| Common operators | ||||||
|---|---|---|---|---|---|---|
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|
a = b |
++a |
+a |
!a |
a == b |
a[b] |
a(...) |