printf 中 double 的正确格式说明符

正确的格式说明符是什么double在 printf 中？是吗%f或者是%lf？我相信这是%f，但我不确定。

代码示例

#include <stdio.h>

int main()
{
   double d = 1.4;
   printf("%lf", d); // Is this wrong?
}

"%f" is the (or at least one) correct format for a double. There is no format for a float, because if you attempt to pass a float to printf, it'll be promoted to double before printf receives it¹. "%lf" is also acceptable under the current standard -- the l is specified as having no effect if followed by the f conversion specifier (among others).

请注意，这是一个地方printf格式字符串与scanf (and fscanf等）格式字符串。对于输出，您传递一个value，将从float to double当作为可变参数传递时。对于输入，您传递一个pointer，这是不提倡的，所以你必须告诉scanf您是否想阅读float or a double， 因此对于scanf, %f意味着你想阅读float and %lf意味着你想阅读double（而且，就其价值而言，long double， 你用%Lf对于任一printf or scanf).

_{1. C99, §6.5.2.2/6: "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." In C++ the wording is somewhat different (e.g., it doesn't use the word "prototype") but the effect is the same: all the variadic parameters undergo default promotions before they're received by the function.}