定制sprintf，值得吗？

Question

下面的代码是从nginx中提取出来的，基本上是重写了sprintf，实际上nginx还重写了一些其他的字符串函数，值得吗？

u_char *
ngx_vslprintf(u_char *buf, u_char *last, const char *fmt, va_list args)
{
    u_char                *p, zero;
    int                    d;
    double                 f, scale;
    size_t                 len, slen;
    int64_t                i64;
    uint64_t               ui64;
    ngx_msec_t             ms;
    ngx_uint_t             width, sign, hex, max_width, frac_width, n;
    ngx_str_t             *v;
    ngx_variable_value_t  *vv;

    while (*fmt && buf < last) {

        /*
         * "buf < last" means that we could copy at least one character:
         * the plain character, "%%", "%c", and minus without the checking
         */

        if (*fmt == '%') {

            i64 = 0;
            ui64 = 0;

            zero = (u_char) ((*++fmt == '0') ? '0' : ' ');
            width = 0;
            sign = 1;
            hex = 0;
            max_width = 0;
            frac_width = 0;
            slen = (size_t) -1;

            while (*fmt >= '0' && *fmt <= '9') {
                width = width * 10 + *fmt++ - '0';
            }


            for ( ;; ) {
                switch (*fmt) {

                case 'u':
                    sign = 0;
                    fmt++;
                    continue;

                case 'm':
                    max_width = 1;
                    fmt++;
                    continue;

                case 'X':
                    hex = 2;
                    sign = 0;
                    fmt++;
                    continue;

                case 'x':
                    hex = 1;
                    sign = 0;
                    fmt++;
                    continue;

                case '.':
                    fmt++;

                    while (*fmt >= '0' && *fmt <= '9') {
                        frac_width = frac_width * 10 + *fmt++ - '0';
                    }

                    break;

                case '*':
                    slen = va_arg(args, size_t);
                    fmt++;
                    continue;

                default:
                    break;
                }

                break;
            }


            switch (*fmt) {

            case 'V':
                v = va_arg(args, ngx_str_t *);

                len = ngx_min(((size_t) (last - buf)), v->len);
                buf = ngx_cpymem(buf, v->data, len);
                fmt++;

                continue;

            case 'v':
                vv = va_arg(args, ngx_variable_value_t *);

                len = ngx_min(((size_t) (last - buf)), vv->len);
                buf = ngx_cpymem(buf, vv->data, len);
                fmt++;

                continue;

            case 's':
                p = va_arg(args, u_char *);

                if (slen == (size_t) -1) {
                    while (*p && buf < last) {
                        *buf++ = *p++;
                    }

                } else {
                    len = ngx_min(((size_t) (last - buf)), slen);
                    buf = ngx_cpymem(buf, p, len);
                }

                fmt++;

                continue;

            case 'O':
                i64 = (int64_t) va_arg(args, off_t);
                sign = 1;
                break;

            case 'P':
                i64 = (int64_t) va_arg(args, ngx_pid_t);
                sign = 1;
                break;

            case 'T':
                i64 = (int64_t) va_arg(args, time_t);
                sign = 1;
                break;

            case 'M':
                ms = (ngx_msec_t) va_arg(args, ngx_msec_t);
                if ((ngx_msec_int_t) ms == -1) {
                    sign = 1;
                    i64 = -1;
                } else {
                    sign = 0;
                    ui64 = (uint64_t) ms;
                }
                break;

            case 'z':
                if (sign) {
                    i64 = (int64_t) va_arg(args, ssize_t);
                } else {
                    ui64 = (uint64_t) va_arg(args, size_t);
                }
                break;

            case 'i':
                if (sign) {
                    i64 = (int64_t) va_arg(args, ngx_int_t);
                } else {
                    ui64 = (uint64_t) va_arg(args, ngx_uint_t);
                }

                if (max_width) {
                    width = NGX_INT_T_LEN;
                }

                break;

            case 'd':
                if (sign) {
                    i64 = (int64_t) va_arg(args, int);
                } else {
                    ui64 = (uint64_t) va_arg(args, u_int);
                }
                break;

            case 'l':
                if (sign) {
                    i64 = (int64_t) va_arg(args, long);
                } else {
                    ui64 = (uint64_t) va_arg(args, u_long);
                }
                break;

            case 'D':
                if (sign) {
                    i64 = (int64_t) va_arg(args, int32_t);
                } else {
                    ui64 = (uint64_t) va_arg(args, uint32_t);
                }
                break;

            case 'L':
                if (sign) {
                    i64 = va_arg(args, int64_t);
                } else {
                    ui64 = va_arg(args, uint64_t);
                }
                break;

            case 'A':
                if (sign) {
                    i64 = (int64_t) va_arg(args, ngx_atomic_int_t);
                } else {
                    ui64 = (uint64_t) va_arg(args, ngx_atomic_uint_t);
                }

                if (max_width) {
                    width = NGX_ATOMIC_T_LEN;
                }

                break;

            case 'f':
                f = va_arg(args, double);

                if (f < 0) {
                    *buf++ = '-';
                    f = -f;
                }

                ui64 = (int64_t) f;

                buf = ngx_sprintf_num(buf, last, ui64, zero, 0, width);

                if (frac_width) {

                    if (buf < last) {
                        *buf++ = '.';
                    }

                    scale = 1.0;

                    for (n = frac_width; n; n--) {
                        scale *= 10.0;
                    }

                    /*
                     * (int64_t) cast is required for msvc6:
                     * it can not convert uint64_t to double
                     */
                    ui64 = (uint64_t) ((f - (int64_t) ui64) * scale + 0.5);

                    buf = ngx_sprintf_num(buf, last, ui64, '0', 0, frac_width);
                }

                fmt++;

                continue;

#if !(NGX_WIN32)
            case 'r':
                i64 = (int64_t) va_arg(args, rlim_t);
                sign = 1;
                break;
#endif

            case 'p':
                ui64 = (uintptr_t) va_arg(args, void *);
                hex = 2;
                sign = 0;
                zero = '0';
                width = NGX_PTR_SIZE * 2;
                break;

            case 'c':
                d = va_arg(args, int);
                *buf++ = (u_char) (d & 0xff);
                fmt++;

                continue;

            case 'Z':
                *buf++ = '\0';
                fmt++;

                continue;

            case 'N':
#if (NGX_WIN32)
                *buf++ = CR;
#endif
                *buf++ = LF;
                fmt++;

                continue;

            case '%':
                *buf++ = '%';
                fmt++;

                continue;

            default:
                *buf++ = *fmt++;

                continue;
            }

            if (sign) {
                if (i64 < 0) {
                    *buf++ = '-';
                    ui64 = (uint64_t) -i64;

                } else {
                    ui64 = (uint64_t) i64;
                }
            }

            buf = ngx_sprintf_num(buf, last, ui64, zero, hex, width);

            fmt++;

        } else {
            *buf++ = *fmt++;
        }
    }

    return buf;
}

IMO 写类似的东西只会造成内存浪费，你的想法是什么？

Answer 1

它是否“值得”是主观的——有很多事情需要考虑:

1. 它比 sprintf 有什么优势？你需要它们吗？
2. 您是否愿意忍受可能存在的任何缺点？
3. 您是否充分理解代码以在发现问题时能够修复它？
4. 它和 sprintf 一样快吗？如果不是，你关心吗？

您可能还想考虑编写一个覆盖函数，添加您需要的任何额外功能，但随后只调用 sprintf，而不是重新实现整个函数。