将指针解引用为循环条件？ [英] Dereferencing a pointer as for-loop condition?

问题描述

< p>我的印象是一个for循环必须包括： for（init; condition; increment）
现在我遇到了这个代码： p>

  char * foo，* bar; 
 char * data = getData（）; 
 
 for（foo = data; * foo; foo = bar + 1）{
 for（bar = foo; * bar; ++ bar）{
 if（bar> ; =& data [1024]）{
 printf（error\\\
）; 
} 
 printf（％s\\\
，foo）; 
} 
  

指针的引用是否为有效条件？如果是，什么时候返回 false ？当它指向NULL？

解决方案

指针的引用是否有效？ p>

在C和C ++中，任何可以转换为 bool 给定上下文可以用作循环或条件语句中的有效条件。表达式 * foo 生成 char 类型的值，可转换为 bool 。

何时返回false？

当表达式求值为零时。所有其他值都被视为 true 。




c> NULL ？

foo char * ，因此当 * foo 时，条件变为 false 是'\0'

I was under the impression a for loop has to consist of: for(init; condition; increment) Now I came across this code:

char *foo, *bar;
char* data = getData();

for (foo = data; *foo; foo = bar + 1) {
        for (bar = foo; *bar; ++bar) {
         if (bar >= &data[1024]) { 
           printf("error\n");           
         }
        printf("%s\n", foo);
}

Is the dereferencing of a pointer a valid condition? If so, when does it return false? When it points to NULL?

解决方案

Is the dereferencing of a pointer a valid condition?

In C and C++, any expression that can be converted to a bool in a given context can be used as a valid condition in a loop or a conditional statement. An expression *foo produces a value of type char, which is convertible to bool.

when does it return false?

When the expression evaluates to zero. All other values are considered true.

When it points to NULL?

foo is a char*, so the condition becomes false when *foo is '\0'

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