procedure SetLength(var S: string; NewLength: Integer);
Sets the length of a string or dynamic-array variable.
S is a Delphi string or dynamic-array variable.
NewLength is the new number of characters or elements in S.
For a short-string variable, SetLength simply sets the length-indicator character (the character at S) to the given value. In this case, NewLength must be a value from 0 through 255.
For a long-string or dynamic-array variable, SetLength reallocates the string or array referenced by S to the given length. Existing characters in the string or elements in the array are preserved, but the content of newly allocated space is undefined. The one exception is when increasing the length of a dynamic array in which the elements are types that must be initialized (strings, Variants, Variant arrays, or records that contain such types). When S is a dynamic array of types that must be initialized, newly allocated space is set to 0 or nil.
For dynamic arrays, SetLength may take more than one-length parameter (up to the number of array dimensions). Each parameter specifies the number of elements along a particular dimension.
Following a call to SetLength, S is guaranteed to reference a unique string or array—that is, a string or array with a reference count of one. If there is not enough memory available to reallocate the variable, SetLength raises an EOutOfMemory exception.