如何在字符串居中功能中忽略某些字符串?

I have a string centring function that centres the given string according to the given width (which is 113 characters):

std::string center(std::string input, int width = 113) { 
    return std::string((width - input.length()) / 2, ' ') + input;
}

I am using a game SDK in order to create a gameserver modification, and this game SDK supports coloured strings in the game's command console, which are denoted using a dollar sign and a number from 0-9 (i.e, $1) and are not printed in the console itself.

The string centring function above treats these markers as part of the total string, so I want to add the total amount of characters these markers take up to the width so that the string is actually centred.

I have tried modifying the function:

std::string centre(std::string input, int width = 113) { 
    std::ostringstream pStream;
    for(std::string::size_type i = 0; i < input.size(); ++i) {
        if (i+1 > input.length()) break;
        pStream << input[i] << input[i+1];
        CryLogAlways(pStream.str().c_str());
        if (pStream.str() == "$1" || pStream.str() == "$2" || pStream.str() == "$3" || pStream.str() == "$4" || pStream.str() == "$5" || pStream.str() == "$6" || pStream.str() == "$7" || pStream.str() == "$8" || pStream.str() == "$9" || pStream.str() == "$0")
            width = width+2;
        pStream.clear();
    }
    return std::string((width - input.length()) / 2, ' ') + input;
}

The goal of the above function is to iterate through the string, add the current character and the next to an ostringstream, and evaluate the ostringstream.

This didn't exactly do as I wanted:

<16:58:57> 8I
<16:58:57> 8IIn
<16:58:57> 8IInnc
<16:58:57> 8IInncco
<16:58:57> 8IInnccoom
<16:58:57> 8IInnccoommi
<16:58:57> 8IInnccoommiin
<16:58:57> 8IInnccoommiinng
<16:58:57> 8IInnccoommiinngg 
<16:58:57> 8IInnccoommiinngg  C
<16:58:57> 8IInnccoommiinngg  CCo
<16:58:57> 8IInnccoommiinngg  CCoon
<16:58:57> 8IInnccoommiinngg  CCoonnn
<16:58:57> 8IInnccoommiinngg  CCoonnnne

(snippet from server log)

Here's a brief summary of the issue:

I think I might be missing how iteration works; what am I missing, and how can I make this function work in the way I want it to?

So, what you are really trying to do is count the instances of $N in your string, where N is a decimal digit. To do this, just look in the string for instances of $ using std::string::find, and then check the next character to see if it is a digit.

std::string::size_type pos = 0;
while ((pos = input.find('$', pos)) != std::string::npos) {
    if (pos + 1 == input.size()) {
        break;  //  The last character of the string is a '$'
    }
    if (std::isdigit(input[pos + 1])) {
        width += 2;
    }
    ++pos;  //  Start next search from the next char
}

In order to use std::isdigit, you need to first:

#include <cctype>

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