Flat Array to `va_list` Workaround

#include <cstdarg>
#include <cstdio>
#include <cstring>

#ifdef _MSC_VER
    #pragma warning(disable:4996)
#endif


inline static void assert(bool condition,char const* msg) {
    if (!condition) printf("%s",msg);
}

inline static void printf_buffer(char const*__restrict format_string, char*__restrict argument_buffer) {
    int num_chars = 0;
    PARSE_CHAR:
        switch (*format_string) {
            case '\0': return;
            case '%': {
                int i = 1;
                char c;
                PARSE_SPECIFIER:
                    c = format_string[i++];
                    switch (c) {
                        case 'd': case 'i':
                        case 'u': case 'o': case 'x': case 'X':
                        case 'f': case 'F': case 'e': case 'E': case 'g': case 'G': case 'a': case 'A':
                        case 'c': case 's': case 'p':
                            goto PRINT_SPECIFIER;
                        case 'n':
                            assert(i==2,"\"%%n\" must contain no intermediary characters!");
                            **reinterpret_cast<int**>(argument_buffer) = num_chars;
                            argument_buffer += sizeof(int*);
                            goto DONE_SPECIFIER;
                        case '%':
                            assert(i==2,"\"%%%%\" must contain no intermediary characters!");
                            putchar('%'); ++num_chars;
                            goto DONE_SPECIFIER;
                        case '\0': assert(false,"Expected specifier before end of string!");
                        default: goto PARSE_SPECIFIER;
                    }
                PRINT_SPECIFIER: {
                    char* temp = new char[i+1];
                    strncpy(temp,format_string,i); temp[i]='\0';
                    #define PRINTBRK(TYPE) num_chars+=printf(temp,*reinterpret_cast<TYPE*>(argument_buffer)); argument_buffer+=sizeof(TYPE); break;
                    switch (c) {
                        case 'd': case 'i': PRINTBRK(int)
                        case 'u': case 'o': case 'x': case 'X': PRINTBRK(unsigned int)
                        case 'f': case 'F': case 'e': case 'E': case 'g': case 'G': case 'a': case 'A': PRINTBRK(double)
                        case 'c': PRINTBRK(char)
                        case 's': PRINTBRK(char const*)
                        case 'p': PRINTBRK(void*)
                        default: assert(false,"Implementation error!");
                    }
                    #undef PRINTBRK
                    delete [] temp;
                }
                DONE_SPECIFIER:
                    format_string += i;
                    break;
            }
            default:
                putchar(*format_string); ++format_string; ++num_chars;
                break;
        }
        goto PARSE_CHAR;
}

template <typename type> inline static void insert(char buffer[], size_t* i, type value) {
    memcpy(buffer+*i,&value, sizeof(type));
    *i += sizeof(type);
}

int main(int /*argc*/, char* /*argv*/[]) {
    char buffer[512];
    size_t i = 0;

    int num_chars;
    insert<double>(buffer,&i, 3.14);
    insert<double>(buffer,&i, 3.14f); //Note: when calling a variadic function; floats get promoted to doubles!  So, be sure we pass in a double.
    insert<int*>(buffer,&i, &num_chars);
    insert<int>(buffer,&i, 12345);
    insert<char const*>(buffer,&i, "Hello world!");

    PrintFormatString("double: %2.4f, float: %+2.4f, getting characters: ->%n, percent: %%, int: %10d, string: \"%s\"\n",buffer);
    printf("Printed %d characters before the marked point:\n",num_chars);
    for (int i=0;i<num_chars;++i) printf(" "); printf("<-");
    getchar();

    return 0;
}