下面的代码是从nginx中提取的，它基本上重写了sprintf，实际上nginx也重写了其他一些字符串函数，值得努力吗？
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;
}
答案 0 :(得分：3)
它是否“值得”是主观的 - 有很多事情需要考虑：
sprintf有什么好处？你需要它们吗？sprintf一样快？如果没有，你关心吗？您可能还需要考虑编写一个封面函数，它可以添加您需要的任何额外功能，但只需调用sprintf，而不是重新实现整个函数。
答案 1 :(得分：1)
我认为这种事情不仅浪费而且有害。该名称包含printf，这将导致合理的人首先看到使用它的代码假设其格式字符串为printf - 兼容。但实际上它们只是printf语义的非常差的近似值。这可能导致极其严重的安全关键错误，如果代码仅出现在非常见用例中，则可能无法检测到这些错误。 C标准具有完全安全且可用的snprintf函数，在需要此功能时应始终使用该函数。并且以“安全”的名义设计这个垃圾的人感到羞耻......