C++ “long double”的格式说明符是什么
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What is format specifier for `long double`
提问by Prasad S Deshpande
I am working on application which works on various flavors of Unix and Windows 32bit and 64bit OS.
我正在开发适用于各种 Unix 和 Windows 32 位和 64 位操作系统的应用程序。
I am using long doubledata type, When I do sprintf()and used long doublewith %lfin it then it works fine with windows does not give any kind of error, however on Solaris platform it gives core dump.
我正在使用long double数据类型，当我sprintf()使用 它long double并%lf在其中使用时，它在 Windows 上运行良好，不会出现任何类型的错误，但是在 Solaris 平台上它会提供核心转储。
Sample code for the same issue is as following.
相同问题的示例代码如下。
void main(){
string size = "16622";
string sizeFact = "20";
long long sizeLongLong = strtoll(size);
int factInt = atoi(sizeFact);
long double sizeLongDouble = (long double) sizeLongLong/pow(2, factInt);
char buf[512];
sprintf(buf, "%.3lf %s", sizeLongDouble, "str");
}
As mentioned above code works fine on windows 32bit and 64bit however for sprintf it gives me core on Solaris.
如上所述，代码在 Windows 32 位和 64 位上运行良好，但是对于 sprintf，它在 Solaris 上为我提供了核心。
I tried type casting in sprintf it worked fine.
我尝试在 sprintf 中进行类型转换，效果很好。
sprintf(buf, "%.3lf %s", (double) sizeLongDouble, "str");
What is the format specifier for long double?
什么是格式说明符long double？
What is the mistake I am making here, am I using wrong format specifier because of which it is giving core?
我在这里犯了什么错误，我是否使用了错误的格式说明符，因为它给出了核心？
Why do I need to type cast one more time in sprintf()?
为什么我需要在 sprintf() 中再输入一次 cast？
采纳答案by Some programmer dude
For long doubleyou should use format "%Lf". Formatting with small L (i.e. "%lf") have no effect on POSIX systems (see the specification).
因为long double你应该使用 format "%Lf"。用小 L 格式化（即"%lf"）对 POSIX 系统没有影响（请参阅规范）。
回答by unwind
The documentationmakes this pretty clear:
L
A following a, A, e, E, f, F, g, or Gconversion corresponds to a long double argument. (C99 > allows %LF, but SUSv2 does not.)
升
甲以下一个，A，E，E，F，F，G，或ģ转换对应于长double参数。（C99 > 允许 %LF，但 SUSv2 不允许。）
So, you should use %Lf.
所以，你应该使用%Lf.
回答by lhcopetti
I would add this as a comment but I cannot do that yet. It is also important to note that you could also use the Exponential 'p' notation for long doublein this way:
我会将此添加为评论，但我还不能这样做。同样重要的是要注意，您还可以long double以这种方式使用指数“p”表示法：
- Fixed-point notation:
%Lf - Exponential-notation:
%Le - p notation:
%La
- 定点符号：
%Lf - 指数符号：
%Le - p符号：
%La
回答by Ivaylo Strandjev
Depending on the compiler I have seen %Lfand %llftry both and see which works. The %lfthat you use is the format specifier for doublenot for long double. I believe on g++you should use %llf, while on visual studio it is %Lf.
根据我所见过的编译器%Lf并%llf尝试两者，看看哪个有效。在%lf您使用是格式说明符double不适合long double。我相信g++你应该使用%llf，而在视觉工作室它是%Lf。
