C演算子

Until C99, 50 operators. Since C11, 51 operators, _Alignof . compound literal [C99] not included in the total.

• 6 bitwise operators:
  • Unary bitwise NOT ~ .
  • Binary operators << , >> , & , ^ , | .
• 5 binary operators:
  • Bitwise left shift << .
  • Bitwise right shift >> .
  • Bitwise AND & .
  • Bitwise exclusive or (XOR) ^ .
  • Bitwise inclusive or (OR) | .
• 3 logical operators:
  • Logical AND && .
  • Logical OR || .
  • Unary not ! .
• 11 assignment operators:
  • Simple assignment = .
  • Compound assignment, augmented assignment, or combined assignment *= , /= , %= , += , -= , <<= , >>= , &= , ^= , |= .
• 6 unary operators:
  • Address of & .
  • Pointer type * .
  • Unary arithmetic + , - , ~ , ! .
• 4 unary arithmetic operators:
  • Plus (integer promotion) + , result is an arithmetic type.
  • Minus (additive inverse) - , result is an arithmetic type.
  • Bitwise NOT ~ , result is integer type.
  • Logical negation NOT ! , result is a scalar type of int
• 13 arithmetic operators:
  • Unary + ( +x ) and - ( -x ).
  • Additive + ( x+y ) and - ( x-y ).
  • Multiplicative * ( x*y ), / ( x/y ) and % ( x%y ).
  • Bitwise ~ ( ~x ), << ( x<<y ), >> ( x>>y ), & ( x&y ), ^ ( x^y ) and | ( x|y ).
• 3 multiplicative operators:
  • Multiplication * .
  • Division / .
  • Modulo % , result is integer type.
• 2 additive operators:
  • Addition + .
  • Subtraction - .
• 6 comparison operators:
  • Equality == , != .
  • Relational < , > , <= , >= .
• 4 relational operators:
  • Less than < .
  • Bigger than > .
  • Less than or equal to <= .
  • Bigger than or equal to >= .
• 2 equality operators:
  • Equal to == .
  • Not equal to != .
• 5 member access:
  • Array subscription [] ( x[y] ).
  • Indirection operator, pointer type * ( *x ).
  • Address operator & ( &x ).
  • Access member of struct or union . ( x.y ).
  • Access member of struct or union using pointer -> ( x->y ).
• 2 prefix, increment and decrement operators: ++prefix and --prefix .
• 2 postfix, increment and decrement operators: postfix++ and postfix-- .
• 7 miscellaneous operators:
  • Comma , .
  • Conditional operator or ternary ? : , x > y ? 1 : 0; .
  • Function call ( ) , x(y,z) .
  • sizeof , result is size in bytes.
  • [C11] _Alignof( type ) , result is the alignment requirement of the type.
  • Conversion, c-style cast: ( type ) x .
  • Compound literal[C99] ( type ){ initializer-list } , the result is a unnamed object.

Notes:

• Compound literal behave as an operator but is not explicit in the standard as part of the group operators, but in this guide is considered an operator.
• Same Symbol Different Operators. The behavior is defined by how it is used:
  • Bitwise AND & vs Address Of & .
  • Multiplication * vs Indirection Operator * (Pointer).
  • Unary Minus - and Unary Plus + vs Additive Operators - and + .
• 💩 Applying comparison operators to Infinite or Not-a-Number (NaN) values will cause an exception. NaN does not compare to anything, even between NaN and NaN. To proper compare use isnan function from <math.h> . To compare an Infinite value use isinf or isfinite macros.
• ⚠️ Arithmetic operators applied to floating-point types may cause NaN or Infinite value.

1. Associativity: Left-to-right
   • () - Function call
   • [] - Array subscripting
   • . - Structure and union member access
   • -> - Structure and union member access through pointer
   • ++ , -- - Suffix/postfix increment and decrement
   • (type){list} - Compound literal [C99]
2. Associativity: Right-to-left
   • ! , ~ - Logical NOT and bitwise NOT
   • ++ , -- - Prefix increment and decrement
   • + , - - Unary plus and minus
   • (type) - Type cast
   • sizeof - Size-of
   • * - Indirection (dereference), pointer syntax
   • & - Address-of
   • _Alignof - Alignment requirement [C11]
3. Associativity: Left-to-right
   • * - Multiplication
   • / - Division
   • % - Modulus
4. Associativity: Left-to-right
   • + - Addition
   • - - Subtraction
5. Associativity: Left-to-right
   • << - Bitwise left shift
   • >> - Bitwise right shift
6. Associativity: Left-to-right
   • < - Less than
   • <= - Less than OR equal to
   • > - Greater than
   • >= - Greater than OR equal to
7. Associativity: Left-to-right
   • == - Equal to
   • != - NOT equal to
8. Associativity: Left-to-right
   • & - Bitwise AND
9. Associativity: Left-to-right
   • ^ - Bitwise XOR (exclusive or)
10. Associativity: Left-to-right
    • | - Bitwise OR (inclusive or)
11. Associativity: Left-to-right
    • && - Logical AND
12. Associativity: Left-to-right
    • || - Logical OR
13. Associativity: Right-to-Left
    • ?: - Ternary conditional. Test your compiler precedence on this one.
14. Associativity: Right-to-Left
    • = - Simple assignment
    • += , -= - Assignment by sum and difference
    • *= , /= , %= - Assignment by product, quotient, and remainder
    • <<= , >>= - Assignment by bitwise left shift and right shift
    • &= , ^= , |= - Assignment by bitwise AND, XOR, and OR
15. Associativity: Left-to-right
    • , - Comma

Notes:

• Precedence and associativity are independent from order of evaluation.
• C language standard doesn't specify operator precedence.
• When parsing an expression, an operator which is listed on the same row will be bound tighter ( as if by parentheses ) to its arguments than any operator that is listed on a row further below it. For example, the expression *p++ is parsed as *(p++) , and not as (*p)++ .
• Operators that are in the same cell (there may be several rows of operators listed in a cell) are evaluated with the same precedence, in the given direction. For example, the expression a=b=c is parsed as a=(b=c) , and not as (a=b)=c because of right-to-left associativity.

Most operators does not change the operands values, but a few do:

• Assignment operators change the left-operand value.
• Increment and decrement operators change the operands value.

This is why some programmers use constant value on the left operand. E.g.: instead of == for equality comparison, the programmer mistakable use = that is the simple assignment, the compiler will not be able to recognize the problem:

if(value = 0){} // 💩, It is valid expression for the compiler

To better mitigate risks, exchange the position and the compiler will be able to output a proper error if this mistake happen.

if(0 = value){} // Compiler output a proper error on this

<iso646.h> define 11 macros, that are alternative spellings for some operators. Why <iso646.h> ? European keyboards are not programming-friendly. Some programmers argue that this make easy to parse by human eyes when heavy use of bitwise operators is done with comparison operators.

References