sys/base/string/appendf.c


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#include "internal.h"

/*
 * appendf will append the given formatted string to our buffer.
 * returns the newly minted string
 */

int
str·appendf(string *s, const byte* fmt, ...)
{
    va_list args;
    va_start(args, fmt);
    int remain = str·cap(*s) - str·len(*s);
    int n      = vsnprintf(*s + str·len(*s), remain + 1, fmt, args);
    va_end(args);

    if(n > remain){
        // If the first write was incomplete, we overwite the data again.
        str·grow(s, n);
        va_list args;
        va_start(args, fmt);
        n = vsnprintf(*s + str·len(*s), n + 1, fmt, args);
        assert(n - remain <= str·cap(*s));
        va_end(args);
    }

    Hdr* h = (Hdr*)(*s - sizeof(Hdr));
    h->len += n;

    return n;
}