1、各平台调用接口

2、接口实现

#if defined(_WIN32)
#include <Windows.h>

#elif defined(__unix__) || defined(__unix) || defined(unix) || (defined(__APPLE__) && defined(__MACH__))
#include <unistd.h>
#include <sys/types.h>
#include <sys/param.h>
#if defined(BSD)
#include <sys/sysctl.h>
#endif

#else
#error "Unable to define getMemorySize( ) for an unknown OS."
#endif

size_t getMemorySize( )
{
#if defined(_WIN32) && (defined(__CYGWIN__) || defined(__CYGWIN32__))
    /* Cygwin under Windows. ------------------------------------ */
    /* New 64-bit MEMORYSTATUSEX isn't available.  Use old 32.bit */
    MEMORYSTATUS status;
    status.dwLength = sizeof(status);
    GlobalMemoryStatus( &status );
    return (size_t)status.dwTotalPhys;

#elif defined(_WIN32)
    /* Windows. ------------------------------------------------- */
    /* Use new 64-bit MEMORYSTATUSEX, not old 32-bit MEMORYSTATUS */
    MEMORYSTATUSEX status;
    status.dwLength = sizeof(status);
    GlobalMemoryStatusEx( &status );
    return (size_t)status.ullTotalPhys;

#elif defined(__unix__) || defined(__unix) || defined(unix) || (defined(__APPLE__) && defined(__MACH__))
    /* UNIX variants. ------------------------------------------- */
    /* Prefer sysctl() over sysconf() except sysctl() HW_REALMEM and HW_PHYSMEM */

#if defined(CTL_HW) && (defined(HW_MEMSIZE) || defined(HW_PHYSMEM64))
    int mib[2];
    mib[0] = CTL_HW;
#if defined(HW_MEMSIZE)
    mib[1] = HW_MEMSIZE;            /* OSX. --------------------- */
#elif defined(HW_PHYSMEM64)
    mib[1] = HW_PHYSMEM64;          /* NetBSD, OpenBSD. --------- */
#endif
    int64_t size = 0;               /* 64-bit */
    size_t len = sizeof( size );
    if ( sysctl( mib, 2, &size, &len, NULL, 0 ) == 0 )
        return (size_t)size;
    return 0L;            /* Failed? */

#elif defined(_SC_AIX_REALMEM)
    /* AIX. ----------------------------------------------------- */
    return (size_t)sysconf( _SC_AIX_REALMEM ) * (size_t)1024L;

#elif defined(_SC_PHYS_PAGES) && defined(_SC_PAGESIZE)
    /* FreeBSD, Linux, OpenBSD, and Solaris. -------------------- */
    return (size_t)sysconf( _SC_PHYS_PAGES ) *
        (size_t)sysconf( _SC_PAGESIZE );

#elif defined(_SC_PHYS_PAGES) && defined(_SC_PAGE_SIZE)
    /* Legacy. -------------------------------------------------- */
    return (size_t)sysconf( _SC_PHYS_PAGES ) *
        (size_t)sysconf( _SC_PAGE_SIZE );

#elif defined(CTL_HW) && (defined(HW_PHYSMEM) || defined(HW_REALMEM))
    /* DragonFly BSD, FreeBSD, NetBSD, OpenBSD, and OSX. -------- */
    int mib[2];
    mib[0] = CTL_HW;
#if defined(HW_REALMEM)
    mib[1] = HW_REALMEM;        /* FreeBSD. ----------------- */
#elif defined(HW_PYSMEM)
    mib[1] = HW_PHYSMEM;        /* Others. ------------------ */
#endif
    unsigned int size = 0;        /* 32-bit */
    size_t len = sizeof( size );
    if ( sysctl( mib, 2, &size, &len, NULL, 0 ) == 0 )
        return (size_t)size;
    return 0L;            /* Failed? */
#endif /* sysctl and sysconf variants */

#else
    return 0L;            /* Unknown OS. */
#endif
}

使用
size_t memorySize = getMemorySize( );