# Locate Run-Time Errors

This topic provides some guidelines for locating the cause of exceptions and run-time errors. Intel® Fortran run-time error messages do not usually indicate the exact source location causing the error.

The following compiler options are related to handling errors and exceptions:

- The check option generates extra code to catch certain conditions at run time. It lets you specify a keyword to check for specific conditions.

  The keyword bounds generates code to perform compile-time and run-time checks on array subscript and character substring expressions. An error is reported if the expression is outside the dimension of the array or the length of the string.

  The keyword uninit generates code for dynamic checks of uninitialized variables. If a variable is read before written, a run-time error routine will be called.

  The keywords noformat and nooutput_conversion reduce the severity level of the associated run-time error to allow program continuation.

  The keyword pointers generates code to test for disassociated pointers and unallocatable arrays.

  The following examples show output messages received when the code was specified using option check[:]pointers.

  Examples

  The following example shows the message received for an allocatable variable that has not been allocated:

      real, allocatable:: a(:)
         !
         ! A is initially unallocated.  To allocate, use:
         !
         !    allocate(a(4))
         !
         ! Because A is unallocated, the next statement will
         ! issue an error in applications built with "check pointers".
         !
         a=17
         print  *,a
         end
      Output 1:
      forrtl: severe (408): fort: (8): Attempt to fetch from allocatable
                                       variable A when it is not allocated

  The following example shows the message received for an unassociated pointer:

         real, pointer:: a(:)
         allocate(a(5))
         a=17
         print  *,a
         deallocate(a)   ! Once A is deallocated, the next statement
                         ! issues an error in an application built
                         ! with "check pointers".
         a=20
         print  *,a
         end

      Output 2:
         17.00000       17.00000       17.00000       17.00000       17.00000
      forrtl: severe (408): fort: (7): Attempt to use pointer A when it is
                                       not associated with a target

  The following example shows the message received for a Cray pointer with a zero value:

         pointer(p,a)
         real, target:: b
         !
         ! P initially has no address assigned to it.  To assign an
         ! address, use:
         !
         !    p=loc(b)
         !
         ! Because P has no address assigned to it, the next
         ! statement will issue an error in an application built
         ! with "check pointers".
         !
         b=17.
         print  *,a
         end
      Output 3:
      forrtl: severe (408): fort: (9): Attempt to use pointee A when its
                                       corresponding integer
                                       pointer P has the value zero

- The traceback option generates extra information in the object file to provide source file traceback information when a severe error occurs at run time. This simplifies the task of locating the cause of severe run-time errors. Without the traceback option, you could try to locate the cause of the error using a map file and the hexadecimal addresses of the stack displayed when a severe error occurs. Certain traceback-related information accompanies severe run-time errors, as described in Traceback.

- The fpe option controls the handling of floating-point arithmetic exceptions (IEEE arithmetic) at run time. If you specify the fpe[:]3 compiler option, all floating-point exceptions are disabled, allowing IEEE exceptional values and program continuation. In contrast, specifying fpe[:]0 stops execution when an exceptional value (such as a NaN) is generated, when floating overflow or divide by zero occur, or when attempting to use a subnormal number, which usually allows you to localize the cause of the error. It also forces underflow to zero.

- The warn and nowarn options control compile-time warning messages, which, in some circumstances, can help determine the cause of a run-time error.

- Linux and macOS

  The -fexceptions option enables C++ exception handling table generation, preventing Fortran routines in mixed-language applications from interfering with exception handling between C++ routines.

- Windows

  The Compilation Diagnostics Options in the IDE control compile-time diagnostic messages. In some circumstances, these messages can help determine the cause of a run-time error.

Parent topic: Run-Time Errors

## See Also

Understand Run-Time Errors
check compiler option
traceback compiler option
fpe compiler option
warn compiler option
fexceptions compiler option