sscanf("0X80.9", "%f", &value) 将值设置为十六进制浮点数而不是浮点数 [英] sscanf("0X80.9", "%f", &value) sets value to a hex float not a float

问题描述

我有一些读取字母值对的代码.可以简化为:

I have some code that reads letter value pairs. It can be simplified as:

float value = 0.0;
sscanf("0X80.9", "%f", &value);

在 Visual Studio 2013 中，值 = 0

In Visual Studio 2013, value = 0

在 Visual Studio 2015 及更高版本中，值 = 128.5625(即十六进制的 0x80 = 十进制的 128)

In Visual Studio 2015 and above, value = 128.5625 (i.e. 0x80 in hex = 128 in decimal)

有人知道为什么会改变吗?更重要的是，有人知道如何让它像以前一样工作吗?

Anyone know why this has changed? More importantly, anyone know how to make it work like it used to?

推荐答案

C99 添加了一个新特性，十六进制浮点常量.它还为 *scanf() 函数添加了新格式.(源代码中的十六进制浮点常量必须有指数部分；对于scanf，指数是可选的.)

C99 added a new feature, hexadecimal floating-point constants. It also added new formats to the *scanf() functions. (A hexadecimal floating-point constant in source code must have an exponent part; for scanf, the exponent is optional.)

scanf 尽可能多地读取与格式一致的输入.对于 1999 之前的 C，这是初始的 "0"；剩下下面的"X80.9".对于 C99，"0X80.9" 有效，并转换为浮点值 128.5625.(格式与 strtof() 接受的格式相同.)

scanf reads as much of the input as it can that's consistent with the format. For pre-1999 C, this is the initial "0"; the following "X80.9"is left. For C99, "0X80.9" is valid, and is converted to the floating-point value 128.5625. (The format is the same as what's accepted by strtof().)

C++ 标准通过引用包含了大部分 C 标准库.直到 c++2012 才更新到 C99 版本的 C 库.

The C++ standard includes most of the C standard library by reference. It didn't update to the C99 version of the C library until c++2012.

很可能 Visual Studio 2015 支持 C++12 或更高版本，而 Visual Studio 2013 不支持.

Most likely Visual Studio 2015 supports C++12 or later, and Visual Studio 2013 doesn't.

由于新行为现在是标准的，我建议调整您的代码来处理它，而不是试图强制执行旧行为.如果有办法让 VS2015 以旧方式运行，则应记录在案.

Since the new behavior is now standard, I suggest adapting your code to deal with it rather than trying to force the old behavior. If there's a way to make VS2015 behave in the old way, it should be documented.

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