64 lines
1.2 KiB
Markdown
64 lines
1.2 KiB
Markdown
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---
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title: Short-Circuit Evaluation
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localeTitle: 短路评估
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---
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# 短路评估
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仅当第一个参数不足以确定表达式的值时，短路评估才包括检查或执行第二个参数。
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您可以使用&&和||进行短路评估运营商。
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## &&运算符的示例：
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```c
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canOpenFile(filename) && openFile(filename); // If you can open the file then open it.
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```
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上面的例子相当于：
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```c
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if ( canOpenFile(filename) ) {
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openFile(filename);
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}
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```
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## 示例包含||运营商：
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```c
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isServerOn || startServer(); // If the server is not on then start it.
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```
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The example above is equivalent to:
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```c
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if ( !isServerOn ) {
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startServer();
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}
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```
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## Keep it all together in real example
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```c
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#include <stdio.h>
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#include <stdlib.h>
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char *getName();
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int main(int argc, char *argv[]) {
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// Get first argument passed via terminal
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char *name = argv[1];
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// If name is not passed via terminal then print message and then get the name
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name || printf("Please give me your name:") && (name = getName());
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printf("Hello %s\n", name);
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}
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char *getName() {
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// Allocate memory
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char *name = malloc(30);
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scanf("%s", name);
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return name;
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}
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```
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