Customized sprintf,is it worth the effort?
The code below is extracted from nginx,which basically rewrites sprintf,in fact nginx also rewrites some other string functions,is it worth the effort?
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++ = '%';
开发者_运维问答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 writing similar stuff only causes waste of memory,your idea?
Whether it's "worth it" is subjective - there are lots of things to consider:
- What advantages does it give over
sprintf? Do you need them? - Are you willing to live with whatever shortcomings may be there?
- Do you understand the code well enough to be able to fix it if problems are found?
- Is it as fast as
sprintf? If not, do you care?
You may also want to consider writing a cover function that adds whatever extra functionality you need but then just calls sprintf, rather than re-implement the entire function.
I think this kind of thing is not only wasteful but actively harmful. The name includes printf, which would lead a reasonable person first seeing code that's using it to assume its format strings are printf-compatible. But in fact they're only a very poor approximation of printf semantics. This could lead to extremely serious, security-critical bugs, which might go undetected if the code only appears in a non-common-usage case. The C standard has a perfectly safe and usable snprintf function which should always be used when this functionality is needed. And shame on whoever designed this junk in the name of "security"...
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