C++ 将 int64_t 转换为双精度
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Convert int64_t to double
提问by kal
int64_t a = 1234;
double d = (double) a;
Is this the recommended way?
这是推荐的方式吗？
回答by Tom
use static_castas strager answers. I recommend againstusing the implicit cast (or even a C-style cast in C++ source code) for a few reasons:
使用static_cast作为strager答案。我建议不要使用隐式转换（甚至 C++ 源代码中的 C 样式转换），原因如下：
- Implicit casts are a common source of compiler warnings, meaning you may be adding noise to the build (either now, or later when better warning flags are added).
- The next maintenance programmer behind you will see an implicit cast, and needs to know if it was intentional behavior or a mistake/bug. Having that
static_castmakes your intentimmediately obvious. static_castand the other C++-style casts are easy forgrepto handle.
- 隐式强制转换是编译器警告的常见来源，这意味着您可能会在构建中添加噪音（现在或稍后添加更好的警告标志时）。
- 您身后的下一个维护程序员将看到一个隐式转换，并且需要知道这是故意行为还是错误/错误。有了这个
static_cast，你的意图就很明显了。 static_cast其他 C++ 风格的类型转换很容易grep处理。
回答by strager
You should use static_castor rely on the implicit cast instead:
您应该使用static_cast或依赖隐式转换：
int64_t a = 1234;
double d = static_cast<double>(a);
double f = a;
回答by Andrew Grant
For POD types both versions do the same thing. Choose the one you prefer and be consistent.
对于 POD 类型，两个版本都做同样的事情。选择您喜欢的一种并保持一致。
I know many people who prefer the former for typing/readability and I tend to agree with this but I can live with either.
我知道很多人更喜欢前者的打字/可读性，我倾向于同意这一点，但我可以接受。
I've heard the "easy to grep for" argument many times but have yet to ever come across a situation where I've needed to grep my codebase for POD casts.
我已经多次听到“易于 grep for”的论点，但还没有遇到过需要为 POD 强制转换我的代码库的情况。
回答by dcw
You can also use the conversion syntax, which is equivalent to a static_cast:
您还可以使用转换语法，它等效于 static_cast：
int64_t a = 1234;
double d = double(a);
This is a useful syntactic construction in that it allows primitive and class types to be treated the same way in template code, either doing a static_cast, for the primitive, or invoking a constructor, for the class type.
这是一个有用的语法构造，因为它允许在模板代码中以相同的方式处理原始类型和类类型，或者为原始类型执行 static_cast，或者为类类型调用构造函数。
