libssh2_knownhost_writefile man page
libssh2_knownhost_writefile — write a collection of known hosts to a file
int libssh2_knownhost_writefile(LIBSSH2_KNOWNHOSTS *hosts,
const char *filename, int type);
Writes all the known hosts to the specified file using the specified file format.
filename specifies what filename to create
type specifies what file type it is, and LIBSSH2_KNOWNHOST_FILE_OPENSSH is the only currently supported format.
Returns a regular libssh2 error code, where negative values are error codes and 0 indicates success.
Added in libssh2 1.2