If the data on the link corresponds to a real number, MLGetInteger32() will round it to an integer.
If the data on the link corresponds to an integer too large to store in a C int on your computer system, then MLGetInteger32() will fail, and return 0.
You can get arbitrary-precision integers by first using IntegerDigits to generate lists of digits, then calling MLGetInteger32List().
MLGetInteger32() returns a nonzero value if the function succeeds.
Use MLError() to retrieve the error code if MLGetInteger32() fails.
MLGetInteger32() is declared in the MathLink header file mathlink.h.