如何更改 stl 的打印精度？
我想使用带有小数位数的 stl 将数字打印到文件中，而不是整体精度。
所以，如果我这样做：
int precision = 16;
std::vector<double> thePoint(3);
thePoint[0] = 86.3671436;
thePoint[1] = -334.8866574;
thePoint[2] = 24.2814;
ofstream file1(tempFileName, ios::trunc);
file1 << std::setprecision(precision)
<< thePoint[0] << "\\"
<< thePoint[1] << "\\"
<< thePoint[2] << "\\";
我会得到这样的数字：
86.36714359999999\-334.8866574\24.28140258789063
我想要的是这样的：
86.37\-334.89\24.28
换句话说，截断两位小数。如果我将精度设置为 4，那么我会得到
86.37\-334.9\24.28
ie，第二个数字被不正确地截断。
我不想显式地操作每个数字来获得截断，特别是因为我似乎偶尔会得到重复的 9 或 0000000001 或类似的东西。
我确信有一些明显的东西，比如使用 printf(%.2f) 或类似的东西，但我不确定如何将其与 stl << 混合使用。和外流。
I want to print numbers to a file using the stl with the number of decimal places, rather than overall precision.
So, if I do this:
int precision = 16;
std::vector<double> thePoint(3);
thePoint[0] = 86.3671436;
thePoint[1] = -334.8866574;
thePoint[2] = 24.2814;
ofstream file1(tempFileName, ios::trunc);
file1 << std::setprecision(precision)
<< thePoint[0] << "\\"
<< thePoint[1] << "\\"
<< thePoint[2] << "\\";
I'll get numbers like this:
86.36714359999999\-334.8866574\24.28140258789063
What I want is this:
86.37\-334.89\24.28
In other words, truncating at two decimal points. If I set precision to be 4, then I'll get
86.37\-334.9\24.28
ie, the second number is improperly truncated.
I do not want to have to manipulate each number explicitly to get the truncation, especially because I seem to be getting the occasional 9 repeating or 0000000001 or something like that that's left behind.
I'm sure there's something obvious, like using the printf(%.2f) or something like that, but I'm unsure how to mix that with the stl << and ofstream.
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使用 std::fixed ，这应该适合你。
Use std::fixed , this should work for you.
尝试
设置定点格式而不是浮点。
（顺便说一下，这不是 STL。它是 iostream。）
……哦！我认为 Kumar 的
std::fixed比我更好。Try
which sets fixed-point format instead of floating-point.
(By the way, this is not STL. It's iostream.)
…Oh! I think Kumar bettered me with
std::fixed.