immediate mode string concatenation

immediate_mode_string_concatenation.cpp

#include <Windows.h> // for OutputDebugString, max

///////////////////////////////////////////////////////////////////////////////////////////////

#define CONCAT_BUFFER_SIZE 256

///////////////////////////////////////////////////////////////////////////////////////////////

struct concat
{
    concat(char* string) : length(0) { operator()(string); }

    concat(int number) : length(0) { operator()(number); }

    concat(float number, int decimals = 2) : length(0) { operator()(number, decimals); }

    ///////////////////////////////////////////////////////////////////////////////////////////

    char buffer[CONCAT_BUFFER_SIZE];
    int  length;

    ///////////////////////////////////////////////////////////////////////////////////////////

    concat& operator()(char* string)
    {
        while (buffer[length++] = *string++);
        length--;
        return *this;
    }

    concat& operator()(int number)
    {
        int neg = number < 0;
        int num = neg ? -number : number;
        length += log10(num) + neg;
        int idx = length;
        buffer[idx--] = 0;
        do {
            buffer[idx--] = '0' + (num % 10);
            num /= 10;
        } while (num);
        if (neg) buffer[idx] = '-';
        return *this;
    }

    concat& operator()(float number, int decimals = 2)
    {
        static double mul[] = { 1, 10, 100, 1000, 10000, 100000, 1000000 };

        int neg = number < 0;
        unsigned long long num = (unsigned long long)(mul[decimals] * (neg ? -number : number) + 0.5);
        length += max(log10(num), decimals + 1) + neg + (decimals > 0);
        int idx = length;
        buffer[idx--] = 0;
        do {
            buffer[idx--] = '0' + (num % 10);
            num /= 10;
            if (idx == length - decimals - 1) buffer[idx--] = '.';
        } while (num || length - idx <= (decimals ? decimals + 2 : 0));
        if (neg) buffer[idx] = '-';
        return *this;
    }

    operator char* ()
    {
        return buffer;
    }

    ///////////////////////////////////////////////////////////////////////////////////////////

    int log10(unsigned long long n)
    {
        if (n < 10000000000) return (n >= 1000000000) ? 10 : (n >= 100000000) ? 9 : (n >= 10000000) ? 8 : (n >= 1000000) ? 7 : (n >= 100000) ? 6 : (n >= 10000) ? 5 : (n >= 1000) ? 4 : (n >= 100) ? 3 : (n >= 10) ? 2 : 1;
        else return (n >= 1000000000000000000) ? 19 : (n >= 100000000000000000) ? 18 : (n >= 10000000000000000) ? 17 : (n >= 1000000000000000) ? 16 : (n >= 100000000000000) ? 15 : (n >= 10000000000000) ? 14 : (n >= 1000000000000) ? 13 : (n >= 100000000000) ? 12 : 11;
    }
};

///////////////////////////////////////////////////////////////////////////////////////////////

void main()
{
    char* name = "slim shady";
    int   line = 1337;
    float temp = -98.567f;

    // attention, slim shady! there's an error in line 1337 : the error code is 666 and the temperature is -98.6 degrees
    OutputDebugStringA(concat("attention, ")(name)("! there's an error in line ")(line)(" : the error code is ")(666)(" and the temperature is ")(temp, 1)(" degrees\n"));
}