如何在PHP中使用加号为正数添加前缀 [英] How to prefix a positive number with plus sign in PHP

问题描述

我需要设计一个函数来返回不变的负数，但是如果该数字已经不存在，则应该在该数字的开头添加一个+符号.

I need to design a function to return negative numbers unchanged but should add a + sign at the start of the number if its already no present.

示例:

Input     Output
----------------
+1         +1
1          +1
-1         -1

它将仅获得数字输入.

It will get only numeric input.

function formatNum($num)
{
# something here..perhaps a regex?
}

此功能在echo/print中将被多次调用，所以越快越好.

This function is going to be called several times in echo/print so the quicker the better.

更新:

谢谢大家的回答.我必须告诉基于sprintf的解决方案非常快.

Thank you all for the answers. I must tell the sprintf based solution is really fast.

推荐答案

您可以将regex用作:

You can use regex as:

function formatNum($num){
    return preg_replace('/^(\d+)$/',"+$1",$num);
}

但是我建议不使用regex进行这种琐碎的事情.最好在以下位置使用 sprintf :

But I would suggest not using regex for such a trivial thing. Its better to make use of sprintf here as:

function formatNum($num){
    return sprintf("%+d",$num);
}

来自 sprintf的PHP手册:

一个可选的符号说明符，用于强制在数字上使用符号(-或+).默认情况下，如果数字为负，则仅对数字使用-号. 该说明符也强制正号附加+号，并已在PHP 4.3.0中添加.

An optional sign specifier that forces a sign (- or +) to be used on a number. By default, only the - sign is used on a number if it's negative. This specifier forces positive numbers to have the + sign attached as well, and was added in PHP 4.3.0.

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