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Sprintf

As explained in Modern C

sprintf is a C standard library function that formats output into a character array without providing a destination-size bound.

sprintf formats output into a character array using the formatting capabilities of printf and fprintf. It places a 0 character at the end and returns the number of characters written before it. section 14.1

Appending formatted numbers

A loop can maintain a pointer to the next buffer position, call sprintf(p, form, nums[i]), and advance p by the returned length before copying a separator. This assumes the destination buffer is large enough. section 14.1

The important safety distinction is:

  • sprintf makes no provision against buffer overflow when the destination is too small. section 14.1
  • snprintf accepts a byte limit, truncates when necessary, and can report the length that would have been written with a zero-size destination. section 14.1

How Modern C covers it

How deep it goes
Explains formatting, termination, return length, and overflow risk, while deferring bounded construction to snprintf.
Examples
Demonstrates sprintnumbers, repeated number formatting, separator copying, and the format string "%#zX".
What it assumes
Assumes familiarity with character buffers, strings, pointers, and printf-style format strings.
What you can do after
Apply it via the C standard library while recognizing when bounded formatting is required.
How it connects
Connects sprintf with printf, fprintf, snprintf, character arrays, and buffer overflow.
Cover of Modern C
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