本文主要是介绍What does `return x ? : 1` mean in C language? [duplicate] stackoverflow,希望对大家解决编程问题提供一定的参考价值,需要的开发者们随着小编来一起学习吧!
#include <stdio.h>
int f(int x)
{return x?:1;
}
int main()
{printf("f %d\n", f(0));printf("f %d\n", f(1));return 0;
}
And got the following output
f 1
f 1
And when I change it to
int f(int x)
{return x?:2;
}
I am getting
f 2
f 1
I just want to know whether this behavior (return 1 if nothing mentioned) is mentioned in the standard.
Answer:
The middle operand in a conditional expression may be omitted. Then if the first operand is nonzero, its value is the value of the conditional expression.
Therefore, the expression
x ? : y
has the value of x
if that is nonzero; otherwise, the value of y
.
This example is perfectly equivalent to
x ? x : y
In this simple case, the ability to omit the middle operand is not especially useful. When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect. Then repeating the operand in the middle would perform the side effect twice. Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.
这篇关于What does `return x ? : 1` mean in C language? [duplicate] stackoverflow的文章就介绍到这儿,希望我们推荐的文章对编程师们有所帮助!