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逻辑运算符对其操作数应用标准布尔代数运算。
Operator | Operator name | Example | Result |
|---|---|---|---|
! | logical NOT | !a | the logical negation of a |
&& | logical AND | a && b | the logical AND of a and b |
|| | logical OR | a || b | the logical OR of a and b |
逻辑 NOT 表达式具有这种形式。
! expression |
|---|
其中
expression | - | an expression of any scalar type |
|---|
逻辑 NOT 运算符具有类型int。它的值是0如果表达式评估为一个比较不等于零的值。它的值是1如果表达式计算出的值等于零。（如此!E相同(0==E)）。
#include <stdbool.h>#include <stdio.h>#include <ctype.h>int main(void){
bool b = !(2+2 == 4); // not true printf("!(2+2==4) = %s\n", b ? "true" : "false");
int n = isspace('a'); // zero if 'a' is a space, nonzero otherwise
int x = !!n; // "bang-bang", common C idiom for mapping integers to [0,1] // (all non-zero values become 1)
char *a[2] = {"nonspace", "space"}; printf("%s\n", a[x]); // now x can be safely used as an index to array of 2 ints}输出：
!(2+2==4) = falsenonspace
逻辑“与”表达式具有这种形式。
lhs && rhs |
|---|
其中
lhs | - | an expression of any scalar type |
|---|---|---|
rhs | - | an expression of any scalar type, which is only evaluated if lhs does not compare equal to 0 |
逻辑 AND 运算符具有类型int和值，1如果 lhs 和rhs 比较不等于零。它具有其他值0（如果lhs或rhs或两者都等于零）。
lhs评估后有一个序列点。如果lhs的结果等于零，则根本不评估rhs（所谓的短路评估）。
#include <stdbool.h>#include <stdio.h>int main(void){
bool b = 2+2==4 && 2*2==4; // b == true
1 > 2 && puts("this won't print");
char *p = "abc"; if(p && *p) // common C idiom: if p is not null // AND if p does not point at the end of the string { // (note that thanks to short-circuit evaluation, this // will not attempt to dereference a null pointer) // ... // ... then do some string processing }}逻辑 OR 表达式具有表格。
lhs || rhs |
|---|
其中
lhs | - | an expression of any scalar type |
|---|---|---|
rhs | - | an expression of any scalar type, which is only evaluated if lhs compares equal to 0 |
如果lhs或rhs比较不等于零，则逻辑或运算符具有类型int和值1。它有价值0否则（如果lhs和rhs比较等于零）。
lhs 评估后有一个序列点。如果lhs的结果不等于零，则根本不评估 rhs（所谓的短路评估）。
#include <stdbool.h>#include <stdio.h>#include <string.h>#include <errno.h>int main(void){
bool b = 2+2 == 4 || 2+2 == 5; // true printf("true or false = %s\n", b ? "true" : "false");
// logical OR can be used simialar to perl's "or die", as long as rhs has scalar type fopen("test.txt", "r") || printf("could not open test.txt: %s\n", strerror(errno));}可能的输出：
true or false = truecould not open test.txt: No such file or directory
C11 standard (ISO/IEC 9899:2011):
6.5.3.3 Unary arithmetic operators (p: 89)
6.5.13 Logical AND operator (p: 99)
6.5.14 Logical OR operator (p: 99)
C99 standard (ISO/IEC 9899:1999):
6.5.3.3 Unary arithmetic operators (p: 79)
6.5.13 Logical AND operator (p: 89)
6.5.14 Logical OR operator (p: 89)
C89/C90 standard (ISO/IEC 9899:1990):
3.3.3.3 Unary arithmetic operators
3.3.13 Logical AND operator
3.3.14 Logical OR operator