C语言 C中“==”运算符的返回值
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Return value of "==" operator in C
提问by Victor Dodon
Can I assume that in C, the "==" operator will always evaluate to 1 if the two values are equal or it can evaluate to other "true" values?
我可以假设在 C 中，如果两个值相等，“==”运算符将始终计算为 1，或者它可以计算为其他“真”值？
struct ss {
int id;
};
struct os {
int sid;
int state;
};
int count(struct ss *s, int state)
{
int num = 0;
// foreach o (of type os*) in a hash table
num += o->state == state && (s ? o->sid == s->id : 1);
return num;
}
So o->sid == s->idwill return always 1 or 0, or it can return other values?
那么o->sid == s->id将始终返回 1 或 0，还是可以返回其他值？
回答by Yu Hao
Can I assume that in C, the "==" operator will always evaluate to 1 if the two values are equal or it can evaluate to other "true" values?
我可以假设在 C 中，如果两个值相等，“==”运算符将始终计算为 1，或者它可以计算为其他“真”值？
Yes, and so does !=><>=<=all the relational operator.
是的，!=><>=<=所有关系运算符也是如此。
C11(ISO/IEC 9899:201x) §6.5.8 Relational operators
C11(ISO/IEC 9899:201x) §6.5.8关系运算符
Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is false.107) The result has type int.
如果指定的关系为真，则每个运算符 <（小于）、>（大于）、<=（小于或等于）和 >=（大于或等于）应产生 1，如果是，则产生 0 false.107) 结果的类型为 int。
回答by Pierre Fourgeaud
From the standard :
从标准：
6.5.8 Relational operators
Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) shall yield 1if the specified relation is true and 0 if it is false. The result has type int.
6.5.9 Equality operators
The ==(equal to) and != (not equal to) operators are analogous to the relational operators except for their lower precedence. Each of the operators yields 1if the specified relation is true and 0 if it is false. The result has type int. For any pair of operands, exactly one of the relations is true.
6.5.8 关系运算符
如果指定的关系为真，则每个运算符 <（小于）、>（大于）、<=（小于或等于）和 >=（大于或等于）应产生1，如果是，则产生 0错误的。结果的类型为int。
6.5.9 等式运算符
的==（等于），！=（不等于）运算符类似于关系运算符除了他们的优先级低。如果指定的关系为真，则每个运算符产生 1，如果为假，则产生 0。结果的类型为int。对于任何一对操作数，只有一个关系为真。
For logical operands (&&, ||) :
对于逻辑操作数 ( &&, ||) ：
6.5.13 Logical AND operator ( or 6.5.14 Logical OR operator )
The &&(or ||) operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it yields 0. The result has type int.
6.5.13 逻辑 AND 运算符（或 6.5.14 逻辑 OR 运算符）
的&&（或||）操作者应得到1，如果两个操作数的比较不等于0; 否则，结果为 0。结果的类型为 int。
You can check the last draft here : http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
你可以在这里查看最后的草稿：http: //www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
Conclusion :
结论 ：
All the equality and relational operator (
==,!=,<,>,<=,>=) return0forfalseand1fortrue.The logical operators (
==,||,!) treat0asfalseand other values astruefor their operands. They also return0asfalseand1astrue.
所有等式和关系运算符 (
==,!=,<,>,<=,>=) 都返回0forfalse和1fortrue。逻辑运算符 (
==,||,!) 将0asfalse和其他值视为true其操作数。它们也返回0asfalse和1astrue。
回答by Jonathan Leffler
The comparison (equality and relational) operators (==, !=, <, >, <=, >=) all return 0 for false and 1 for true — and no other values.
比较（相等和关系）运算符 ( ==, !=, <, >, <=, >=) 都返回 0 表示 false 和 1 表示真 - 并且没有其他值。
The logical operators &&, ||and !are less fussy about their operands; they treat 0 as false and any non-zero value as true. However, they also return only 0 for false and 1 for true.
逻辑运算符&&,||和!对其操作数不那么挑剔；他们将 0 视为假，将任何非零值视为真。但是，它们也只返回 0 表示假，返回 1 表示真。
回答by Andreas Fester
Can I assume that in C, the "==" operator will always evaluate to 1 if the two values are equal or it can evaluate to other "true" values?
我可以假设在 C 中，如果两个值相等，“==”运算符将始终计算为 1，或者它可以计算为其他“真”值？
Yes, for a standard compliant compiler, this assumption is correct:
是的，对于符合标准的编译器，这个假设是正确的：
Programming languages — C, §6.5.9 Equality operators(http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf):
编程语言 - C，§6.5.9 相等运算符（http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf）：
Each of the operators yields 1 if the specified relation is true and 0 if it is false. The result has type int.
如果指定的关系为真，则每个运算符产生 1，如果为假，则产生 0。结果的类型为 int。
