c - 请帮助我了解 "strcmp"

Question

关闭。此题需要 details or clarity 。目前不接受答案。

---

想要改进这个问题吗？通过 editing this post 添加详细信息并澄清问题.

已关闭 8 年前。

Improve this question

我有一段 C 代码，我想在输入一些字符串(例如“up”)时询问。跳转到代码如下:(strcmp(pdirection,"up")==0)
那么，什么意思呢，我特别不明白==0

代码片段是通过引用位置调用的。

Answer 1

来自manual

int strcmp(const char *s1, const char *s2);

The strcmp() and strncmp() functions return an integer less than, equal to, or greater than zero if s1 (or the first n bytes thereof) is found, respectively, to be less than, to match, or be greater than s2.

因此，如果两个字符串相等，则 strcmp() 返回 0

== 是等于运算符，它检查两边的值是否相等。让我们看看 C 标准怎么说

6.5.9

equality-expression == relational-expression

3 The == (equal to) and != (not equal to) operators are analogous to the relational operators except for their lower precedence.108) Each of the operators yields 1 if 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.

您的代码可能是

if( strcmp(pdirection,"up") == 0 )
    do_something;

因此，如果 pdirection 中存储的字符串等于 "up"，则函数 strcmp() 将返回 0，并且== 0 部分检查该值是否等于 0，如果等于 0，则完成 do_something。