如何在C++中读取位数较多的浮点数？
当我尝试从文件中读取浮点数时遇到问题。我需要读取一行中给出的 3 个浮点数，如下所示：
v -30.50889491515995 -31.95820181187489 0
（我正在从 Rhinoceros 的 .obj 文件进行解析器）
这是我的代码（在此之前我读取一个字符串以查看是否是“v”）：
fstream f(name.c_str());
...
f>>p.x>>p.y>>p.z;
name 是之前从标准输入读取的字符串。
P是一个结构体：
typedef struct Point{
double x;
double y;
double z;
}Point;
问题是读取到的数据是：
-30.5089 -31.9582 0
而不是
-30.50889491515995 -31.95820181187489 0
它四舍五入到小数点后 4 位，我不想要这样！
我尝试使用 fscanf 进行读取，但无法向其发送 fstream 对象。像这样的事情：
fscanf(f,"%f %f %f",p.x,p.y,p.z);
我也尝试过这个，但它不起作用：
f>>setprecision(10)>>fixed>>p.x>>p.y>>p.z;
关于如何避免这种情况的任何想法？我需要更精确的顶点坐标！
非常感谢。
I'm having issues when I try to read a float number from a file. I need to read 3 float numbers given in a line like this:
v -30.50889491515995 -31.95820181187489 0
(I'm doing a parser from a .obj file from Rhinoceros)
Here is my code (before this I read a string to see if is a 'v'):
fstream f(name.c_str());
...
f>>p.x>>p.y>>p.z;
name is a string readed before from standard input.
P is a struct:
typedef struct Point{
double x;
double y;
double z;
}Point;
The problem is that the data readed is:
-30.5089 -31.9582 0
instead of
-30.50889491515995 -31.95820181187489 0
It rounds at 4 decimals, and I don't want that!
I tried to read with fscanf but I can't send it a fstream object. Something like this:
fscanf(f,"%f %f %f",p.x,p.y,p.z);
I also tried this, but it didn't work:
f>>setprecision(10)>>fixed>>p.x>>p.y>>p.z;
Any ideas of how to avoid this? I need more precision in the vertex coordinates!
Thank you very much.
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评论（2）
C++ 总是以全精度输入数字，但您需要指定显示的精度（即输出值时）：
输出：
C++ always inputs the numbers with full precision, but you need to specify the precision for display (i.e. when outputting the values):
output:
set precision应该做你想做的事情。你说这不起作用——你从中得到了什么？您是否尝试在调试器中运行它？是否有可能是输入不正确？
setprecisionshould do what you are wanting to do. You said it didn't work--what did you get out of it?Did you try running it in a debugger? Is it possible that it is not being input properly?