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A comment on C Strings and my slow descent to madness. Parent comment

Re:C Strings and my slow descent to madness by PaulDavisThe1st on Friday April 07, 2023 @12:25AM (#35478024)
no, because the size argument is only an upper bound on how many bytes can be written into the destination.

   snprintf (huge_buf, huge_buffer_size, "%d", 1);
will write two bytes into huge_buf, regardless of huge_buffer_size (assuming it is 2 or larger).
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Re:C Strings and my slow descent to madness by saagarjha on Friday April 07, 2023 @03:45AM (#35479214)
It’s in the other direction, snprintf(small_buf, small_size, “%s”, huge_string) will need to iterate the whole string.
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Re:C Strings and my slow descent to madness by PaulDavisThe1st on Friday April 07, 2023 @09:50AM (#35481539)
why? snprintf() will just write as many bytes from huge_string as necessary, up to the smaller of small_size and strlen (huge_string).

what makes you believe it will iterate the whole of huge_string?

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Re:C Strings and my slow descent to madness by saagarjha on Friday April 07, 2023 @10:59PM (#35490055)
Quoth the standard:

> The snprintf function returns the number of characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if an encoding error occurred.

In essence it needs to return strlen of huge_string even though very little of it was actually written.

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Re:C Strings and my slow descent to madness by PaulDavisThe1st on Saturday April 08, 2023 @12:34AM (#35490562)
Well that's pretty fucked up. I note that the GNU C library docs say this:

> Attention: In versions of the GNU C Library prior to 2.1 the return value is the number of characters stored, not including the terminating null; unless there was not enough space in s to store the result in which case -1 is returned. This was changed in order to comply with the ISO C99 standard.

ISO C99 needs a kick in the head. Yes, there is a use case for this return value (buffer wasn't large enough, reallocate and try it again). But wow, own goal team!

Thanks for this. I had no idea that C99 had defined this so stupidly.

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