PCRE - Perl-compatible regular expressions .rs #include <pcre.h>

 int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output,  " PCRE_SPTR32 input, int length, int *host_byte_order,"  " int keep_boms);" 

. . .rs This function, which exists only in the 32-bit library, converts a UTF-32 string to the correct order for the current host, taking account of any byte order marks (BOMs) within the string. Its arguments are: output pointer to output buffer, may be the same as input input pointer to input buffer length number of 32-bit units in the input, or negative for a zero-terminated string host_byte_order a NULL value or a non-zero value pointed to means start in host byte order keep_boms if non-zero, BOMs are copied to the output string The result of the function is the number of 32-bit units placed into the output buffer, including the zero terminator if the string was zero-terminated.

If host_byte_order is not NULL, it is set to indicate the byte order that is current at the end of the string.

There is a complete description of the PCRE native API in the HREF
pcreapi
page and a description of the POSIX API in the HREF
pcreposix
page.