#define AFTERX(x) X_ ## x
#define XAFTERX(x) AFTERX(x)
#define TABLESIZE 1024
#define BUFSIZE TABLESIZE

#define X_BUFSIZE 111110 + 1
const int \CPP_TEST1 = AFTERX(BUFSIZE); // expands to X_BUFSIZE

#define X_1024    222221 + 1
const int \CPP_TEST2 = XAFTERX(BUFSIZE); // expands to X_1024