# D. Run time errors

Applications generated by Free Pascal might generate Run time error when certain abnormal conditions are detected in the application. This appendix lists the possible run time errors and gives information on why they might be produced.

1 Invalid function number
  An invalid operating system call was attempted.

2 File not found
  Reported when trying to erase, rename or open a non-existent file.

3 Path not found
  Reported by the directory handling routines when a path does not exist or is invalid. Also reported when trying to access a non-existent file.

4 Too many open files
  The maximum number of currently opened files by your process has been reached. Certain operating systems limit the number of files which can be opened concurrently, and this error can occur when this limit has been reached.

5 File access denied
  Permission accessing the file is denied. This error might be caused by several reasons:
  - Trying to open for writing a file which is read only, or which is actually a directory.
  - File is currently locked byanother process.
  - Trying to create a new file, or directlry while a file or directory of the same name already exists.
  - Trying to read from a file which was opened in write only mode.
  - Trying to write from a file which was opened in read only mode.
  - Trying to remove a directory or file while it is not possible.
  - No permission to access the file or directory.

6 Invalid file handle
  If this happens, the file variable you are using is trashed; it indicates that your memory is corrupted.

12 Invalid file access code
  Reported when a reset or rewrite is called with an invalid `FileMode` value.

15 Invalid drive number
  The number given to the `Getdir` or `ChDir` function specifies a non-existent disk.

16 Cannot remove current directory
  Reported when trying to remove the currently active directory.

17 Cannot rename across drives
  You cannot rename a file such that it would end up on another disk or partition.

100 Disk read error
  An error occurred when reading from disk. Typically when you try to read past the end of a file.

101 Disk write error
  Reported when the disk is full, and you're trying to write to it.

102 File not assigned
  This is reported by `Reset`, `Rewrite`, `Append`, `Rename` and varErase, if you call them with an unassigned file as a parameter.

103 File not open
  Reported by the following functions : Close , Read, Write, Seek, EOf, FilePos, FileSize, Flush, BlockRead, and BlockWrite if the file is not open.

104 File not open for input
  Reported by Read, BlockRead, Eof, Eoln, SeekEof or SeekEoln if the file is not opened with Reset.

105 File not open for output
  Reported by write if a text file isn't opened with Rewrite.

106 Invalid numeric format
  Reported when a non-numeric value is read from a text file, when a numeric value was expected.

150 Disk is write-protected
  (Critical error, DOS only.)
151 Bad drive request struct length
  (Critical error, DOS only.)
152 Drive not ready
  (Critical error, DOS only.)
154 CRC error in data
  (Critical error, DOS only.)
156 Disk seek error
  (Critical error, DOS only.)
157 Unknown media type
  (Critical error, DOS only.)
158 Sector Not Found
  (Critical error, DOS only.)
159 Printer out of paper
  (Critical error, DOS only.)
160 Device write fault
  (Critical error, DOS only.)
161 Device read fault
  (Critical error, DOS only.)
162 Hardware failure
  (Critical error, DOS only.)
200 Division by zero
  The application attempted to divide a number by zero.
201 Range check error
  If you compiled your program with range checking on, then you can get this error in the following cases:
  1. An array was accessed with an index outside its declared range.
  2. Trying to assign a value to a variable outside its range (for instance a enumerated type).
202 Stack overflow error
  The stack has grown beyond its maximum size (in which case the size of local variables should be reduced to avoid this error), or the stack has become corrupt. This error is only reported when stack checking is enabled.
203 Heap overflow error
  The heap has grown beyond its boundaries. This is caused when trying to allocate memory exlicitly with `new`, `getmem` or `reallocmem`, or when a class or object instance is created and no memory is left. Please note that, by default, Free Pascal provides a growing heap, i.e. the heap will try to allocate more memory if needed. However, if the heap has reached the maximum size allowed by the operating system or hardware, then you will get this error.
204 Invalid pointer operation
  This you will get if you call dispose or Freemem with an invalid pointer (notably, `Nil`)
205 Floating point overflow
  You are trying to use or produce too large real numbers.
206 Floating point underflow
  You are trying to use or produce too small real numbers.
207 Invalid floating point operation
  Can occur if you try to calculate the square root or logarithm of a negative number.
210 Object not initialized
  When compiled with range checking on, a program will report this error if you call a virtal method without having initialized the VMT.
211 Call to abstract method
  Your program tried to execute an abstract virtual method. Abstract methods should be overridden, and the overriding method should be called.
212 Stream registration error
  This occurs when an invalid type is registered in the objects unit.
213 Collection index out of range
  You are trying to access a collection item with an invalid index (`objects` unit).
214 Collection overflow error
  The collection has reached its maximal size, and you are trying to add another element (`objects` unit).
215 Arithmetic overflow error
  This error is reported when the result of an arithmetic operation is outside of its supported range. Contrary to Turbo Pascal, this error is only reported for 32-bit or 64-bit arithmetic overflows. This is due to the fact that everything is converted to 32-bit or 64-bit before doing the actual arithmetic operation.
216 General Protection fault
  The application tried to access invalid memory space. This can be caused by several problems:
  1. Deferencing a `nil` pointer
  2. Trying to access memory which is out of bounds (for example, calling `move` with an invalid length).

217 Unhandled exception occurred
  An exception occurred, and there was no exception handler present. The sysutils unit installs a default exception handler which catches all excpetions and exits gracefully.

219 Invalid typecast

  Thrown when an invalid typecast is attempted on a class using the `as` operator.

227 Assertion failed error
  An assertion failed, and no AssertErrorProc procedural variable was installed.