dynamic_string.c

#include "common.h"
#include "dynamic_string.h"

#define INITIAL_BUF_LEN 16

void string_init(String *s)
{
    s->buf = emalloc(INITIAL_BUF_LEN, "string init");
    s->buf_len = INITIAL_BUF_LEN;
    s->len = 0;
    s->buf[0] = '\0';
}

void string_free(String *s)
{
    free(s->buf);
}

// For ge_pow_2(), just to be pedantic
static_assert(sizeof(unsigned long long) >= sizeof(size_t),
  "ge_pow_2() argument might overflow");

void string_set(String *s, const char *format, ...)
{
    va_list ap;

    va_start(ap, format);
    string_set_v(s, format, ap);
    va_end(ap);
}

void string_set_v(String *s, const char *format, va_list ap)
{
    s->len = 0;
    string_append_v(s, format, ap);
}

void string_append(String *s, const char *format, ...)
{
    va_list ap;

    va_start(ap, format);
    string_append_v(s, format, ap);
    va_end(ap);
}

void string_append_v(String *s, const char *format, va_list ap)
{
    va_list ap_copy;
    size_t new_len;

    // The first vsnprintf() will trash 'ap', so keep a copy in case we need to
    // repeat the operation
    va_copy(ap_copy, ap);

    new_len = s->len +
      vsnprintf(s->buf + s->len, s->buf_len - s->len, format, ap);
    if (new_len + 1 > s->buf_len) {
        // The resulting string won't fit in the buffer. Grow the buffer to the
        // next power of two that can accommodate it.
        s->buf_len = ge_pow_2(new_len + 1);
        s->buf = erealloc(s->buf, s->buf_len, "string grow");

        // We should be good now. (Though maybe there's something extremely
        // obscure involving e.g. writing to an argument with %n as well as
        // using that value earlier on in the variable argument list that could
        // break this.)
        vsprintf(s->buf + s->len, format, ap_copy);
    }
    s->len = new_len;

    va_end(ap_copy);
}

char *string_get(String *s)
{
    return s->buf;
}

char *string_get_copy(String *s)
{
    return memcpy(emalloc(s->len + 1, "string copy"), s->buf, s->len + 1);
}

size_t string_len(String *s)
{
    return s->len;
}