I have a struct that contains a string and a length:
typedef struct string {
char* data;
size_t len;
} string_t;
Which is all fine and dandy. But, I want to be able to output the contents of this struct using a printf-like function. data may not have a nul terminator (or have it in the wrong place), so I can't just use %s. But the %.*s specifier requires an int, while I have a size_t.
So the question now is, how can I output the string using printf?
Assuming that your string doesn't have any embedded NUL characters in it, you can use the %.*s specifier after casting the size_t to an int:
string_t *s = ...;
printf("The string is: %.*s\n", (int)s->len, s->data);
That's also assuming that your string length is less than INT_MAX. If you have a string longer than INT_MAX, then you have other problems (it will take quite a while to print out 2 billion characters, for one thing).
int
size_t anyway?"
int instead of size_t because it's for backwards compatibility with code that was written before the C language was standardized, before the type size_t even existed.A simple solution would just be to use unformatted output:
fwrite(x.data, 1, x.len, stdout);
for (size_t i, remaining = x.len;
remaining > 0 && (i = fwrite(x.data, 1, remaining, stdout)) > 0;
remaining -= i) {
}
(Edit: fwrite does indeed write the entire requested range on success; looping is not needed.)
Be sure that x.len is no larger than SIZE_T_MAX.
%i).
snprintf? You can use memcpy to write to a memory location rather than a file...memcpy to copy over the string, and then use snprintf to output the number at the location I want. Not as great as just doing it all in one go, I think...%.*s is preferable.%.*s ignore null bytes?how can I output the string using printf?
In a single call? You can't in any meaningful way, since you say you might have null terminators in strange places. In general, if your buffer might contain unprintable characters, you'll need to figure out how you want to print (or not) those characters when outputting your string. Write a loop, test each character, and print it (or not) as your logic dictates.
size_tto anint, provided the value fits...intthat's going to be one interestingprintfcall :-)) Should check though since it could overflow.datamight contain non-printable characters (like a null character), you don't want%sat all. Write a loop.