什么是％f和％LF在C之间的区别？ [英] What is the difference between %f and %lf in C?
问题描述
我看到一个C的例子，这两个参数在C的书，但作者没有详细说明什么，两者之间的区别是。我知道，％F 指定一个float应该取代其位置。我试图寻找这件事，但有一个很难试图找到该W符号。关于％LF ？
I saw these two parameters in a C example in a C book but the author didn't elaborate what the difference between the two are. I know that %f specifies that a float should take its place. I tried looking this up but had a hard time trying to find this w symbols. What about %lf?
推荐答案
有在的printf 家庭没有区别。在ISO C11标准（下面的所有引用来自C11），截面 7.21.6.1 fprintf函数，段落 / 7 状态，对于→修改（我的粗体）：
There is no difference in the printf family. The ISO C11 standard (all references below are from C11), section 7.21.6.1 The fprintf function, paragraph /7 states, for the l modifier (my bold):
指定后续的D，I，O，U，X，或X转换说明应用于long int或unsigned long int型参数;其后面的n转换说明适用于指向一个长整型参数;后续的c转换说明应用于wint_t参数;后续的s转换说明适用于一个指向wchar_t参数; 或有不影响后面的a，A，E，E，F，F，G，或G转换说明。
Specifies that a following d, i, o, u, x, or X conversion specifier applies to a long int or unsigned long int argument; that a following n conversion specifier applies to a pointer to a long int argument; that a following c conversion specifier applies to a wint_t argument; that a following s conversion specifier applies to a pointer to a wchar_t argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion specifier.
它并不需要修改˚F说明的原因是因为符的已的表示双，从段落 / 8 ：
The reason it doesn't need to modify the f specifier is because that specifier already denotes a double, from paragraph /8 of that same section:
再presenting一个浮点数双参数转换为十进制表示在样式...
A double argument representing a floating-point number is converted to decimal notation in the style ...
这是与事实，继在函数原型的椭圆参数是受默认参数提升为每节 6.5.2.2函数调用，段落<$办C $ C> / 7 ：
That has to do with the fact that arguments following the ellipse in the function prototype are subject to default argument promotions as per section 6.5.2.2 Function calls, paragraph /7:
...在一个函数原型声明符引起的参数类型转换到最后声明参数后，停止省略号。默认参数提升是在尾随参数执行。
... The ellipsis notation in a function prototype declarator causes argument type conversion to stop after the last declared parameter. The default argument promotions are performed on trailing arguments.
由于的printf （和它的整个家庭）的家庭被声明为 INT的printf（为const char *限制格式，...）; 用省略号表示法，该规则适用于这里。默认参数促销活动将在第 6.5.2.2函数调用，段落 / 6 ：
Since printf (and it's entire family) family is declared as int printf(const char * restrict format, ...); with the ellipsis notation, that rule applies here. The default argument promotions are covered in section 6.5.2.2 Function calls, paragraph /6:
如果它表示所调用的函数的前pression有一个类型不包括样机，整数促销活动每个参数执行，和有float类型的参数都提升到两倍。这些被称为默认参数促销活动。
If the expression that denotes the called function has a type that does not include a prototype, the integer promotions are performed on each argument, and arguments that have type float are promoted to double. These are called the default argument promotions.
对于 scanf函数系列，它要求使用的双击而非浮动。第 7.21.6.2 fscanf函数/ 11 ：
For the scanf family, it mandates the use of a double rather than a float. Section 7.21.6.2 The fscanf function /11:
指定后续的D，I，O，U，X，X或n转换说明适用于有类型的指针参数传递给long int或unsigned long int类型; 其后面的a，A，E，E，F，F，G，或G转换符适用于有类型的指针参数为双; 或后续的c，S或[转换符适用于有类型的指针参数传递给wchar_t的。
Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to long int or unsigned long int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to double; or that a following c, s, or [ conversion specifier applies to an argument with type pointer to wchar_t.
这会修改 / 12 该节中规定，对于第％F ：
This modifies the /12 paragraph of that section that states, for %f:
匹配任选签署浮点数，无穷大或NaN，其格式是相同的预期的的strtod函数的目标序列。相应参数应为指针浮动。
Matches an optionally signed floating-point number, infinity, or NaN, whose format is the same as expected for the subject sequence of the strtod function. The corresponding argument shall be a pointer to floating.
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