If required_version is lower than or equal to the version number of the
libssh2 in use, the version number of libssh2 is returned as a pointer to a
zero terminated string.
The required_version should be the version number as constructed by the
LIBSSH2_VERSION_NUM define in the libssh2.h public header file, which is a 24
bit number in the 0xMMmmpp format. MM for major, mm for minor and pp for patch
number.
RETURN VALUE
The version number of libssh2 is returned as a pointer to a zero terminated
string or NULL if the required_version isn't fulfilled.
EXAMPLE
To make sure you run with the correct libssh2 version:
if (!libssh2_version(LIBSSH2_VERSION_NUM)) {
fprintf (stderr, "Runtime libssh2 version too old!");
exit(1);
}