Question

The compiler doesn’t know where stat.h is?

Error:
c:\Projects\ADC_HCI\mongoose.c(745) : error C2079: ‘st’ uses undefined struct ‘_stat64’

#include <sys/types.h>
#include <sys/stat.h>

static int
mg_stat(const char *path, struct mgstat *stp)
{
    struct  _stat64 st; //<-- ERROR

    int     ok;
    wchar_t     wbuf[FILENAME_MAX];

    to_unicode(path, wbuf, ARRAY_SIZE(wbuf));
    if (_wstat64(wbuf, &st) == 0) {
        ok = 0;
        stp->size = st.st_size;
        stp->mtime = st.st_mtime;
        stp->is_directory = S_ISDIR(st.st_mode);
    } else {
        ok = -1;
    }

    return (ok);
}  

…downloaded the files straight from the source.

Answer 1

See MSDN: _wstat64 takes a parameter of struct __stat64 (with two underscores). Redeclare your variable st to be of type struct __stat64.