KCGI_BUF_PRINTF(3) Library Functions Manual KCGI_BUF_PRINTF(3)

kcgi_buf_printf —
put variable content into a kcgi buffer

library “libkcgi”

#include <sys/types.h>
#include <stdarg.h>
#include <stdint.h>
#include <kcgi.h>

enum kcgi_err
kcgi_buf_puts(struct kcgi_buf *buf, const char *fmt, ...);

Appends output according to the given fmt to a buffer buf. The format is as for printf(3). Buffers must be initialised to zero with memset(3) prior to first use.

Returns an enum kcgi_err indicating the error state.
Success (not an error).
Internal memory allocation failure.
The output connection has been terminated. For FastCGI connections, the current connection should be released with khttp_free(3) and parse loop reentered.
The connection is still expecting headers with khttp_head(3). Indicates that khttp_body(3) did not return with success or was not invoked. For FastCGI connections, the current connection should be released with khttp_free(3) and parse loop reentered.
Internal system error writing to the output stream.

The following creates a simple NUL-terminated buffer and outputs its contents. It does not perform any error checking. 
struct kcgi_buf buf;

memset(&buf, 0, sizeof(struct kcgi_buf));
kcgi_buf_printf(&buf, "number %d", 1);
puts(buf.buf); /* Emits "number 1" */
free(buf.buf);

kcgi_buf_putc(3), kcgi_buf_puts(3), kcgi_buf_write(3)

Written by Kristaps Dzonsons <kristaps@bsd.lv>.
March 22, 2020 OpenBSD 6.5