[英]error “expression result is unused” in c++
I have some code like: 我有一些类似的代码:
double calculate_self_term(double area) {
double corr = 2.0 * sqrtpi / sqrt(area);
return calculate_reciprocal(0, 0, 0) + self_energy + corr;
}
where self_energy
is defined at the beginning: 在
self_energy
处定义了self_energy
地方:
#define self_energy -2.0 * alpha / sqrtpi;
Then I got an error: expression result is unused for the variable corr
. 然后我得到一个错误:变量
corr
表达式结果未使用 。
Don't use macros for such things. 不要将宏用于此类操作。
With your definition: 根据您的定义:
#define self_energy -2.0 * alpha / sqrtpi;
Your code substitutes to: 您的代码替代为:
return calculate_reciprocal(0, 0, 0) + -2.0 * alpha / sqrtpi; + corr;
At which point the issue should be obvious - you have this +corr
expression statement, after your return
statement, which is doing nothing. 在这一点上,问题应该很明显-在
return
语句之后,您有这个+corr
表达式语句,它什么也没做。
If you didn't use the macro, you wouldn't have run into such an issue. 如果您不使用宏,则不会遇到这样的问题。 Don't use macros for such things.
不要将宏用于此类操作。 This should probably just be a function:
这可能只是一个函数:
constexpr auto self_energy(double alpha) { return -2.0 * alpha / sqrtpi; }
// ...
return calculate_reciprocal(0, 0, 0) + self_energy(alpha) + corr;
Remove the semicolon in the macro 删除宏中的分号
#define self_energy -2.0 * alpha / sqrtpi;
^^^
and write it like 像这样写
#define self_energy ( -2.0 * alpha / sqrtpi )
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