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@@ -480,6 +480,15 @@ Const
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\end{verbatim}
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The order of the fields in a constant record needs to be the same as in the type declaration,
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otherwise a compile-time error will occur.
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+
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+\begin{remark}
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+It should be stressed that typed constants are initialized at program start.
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+This is also true for {\em local} typed constants. Local typed constants are
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+also initialized at program start. If their value was changed during previous
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+invocations of the function, they will retain their changed value, i.e. they
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+are not initialized each time the function is invoked.
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+\end{remark}
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+
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% resource strings
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\section{Resource strings}
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@@ -799,7 +808,6 @@ conversions. Note, however, that the result of an expression that contains
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ansistrings and short strings will always be an ansistring.
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\subsection{Short strings}
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-
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A string declaration declares a short string in the following cases:
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\begin{enumerate}
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@@ -808,7 +816,6 @@ will always be a short string declaration.
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\item If the switch is on \var{\{\$H+\}}, and there is a length
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specifier, the declaration is a short string declaration.
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\end{enumerate}
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-
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The predefined type \var{ShortString} is defined as a string of length 255:
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\begin{verbatim}
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ShortString = String[255];
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@@ -829,21 +836,25 @@ Type
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\var{StreetString} can contain up to 255 characters.
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\subsection{Ansistrings}
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-
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-If the \var{\{\$H\}} switch is on, then a string definition that doesn't
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-contain a length specifier, will be regarded as an ansistring.
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-
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Ansistrings are strings that have no length limit. They are reference
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-counted. Internally, an ansistring is treated as a pointer.
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+counted and null terminated. Internally, an ansistring is treated as
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+a pointer. This is all handled transparantly, i.e. they can be manipulated
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+as a normal short string. Ansistrings can be defined using the predefined
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+\var{AnsiString} type.
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+
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+If the \var{\{\$H\}} switch is on, then a string definition using the
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+regular \var{String} keyword and that doesn't contain a length specifier,
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+will be regarded as an ansistring as well. If a length specifier is present,
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+a short string will be used, regardless of the \var{\{\$H\}} setting.
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-If the string is empty (\var{''}), then the pointer is nil.
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-If the string is not empty, then the pointer points to a structure in
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-heap memory.
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+If the string is empty (\var{''}), then the internal pointer representation
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+of the string pointer is \var{Nil}. If the string is not empty, then the
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+pointer points to a structure in heap memory.
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-It is possible to typecast an ansistring to a pchar.
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-If the string is empty (so the pointer is nil) then the compiler
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-makes sure that the typecasted pchar will point to a null byte. AnsiStrings
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-can be unlimited in length.
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+The internal representation as a pointer, and the automatic null-termination
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+make it possible to typecast an ansistring to a pchar. If the string is empty
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+(so the pointer is nil) then the compiler makes sure that the typecasted
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+pchar will point to a null byte.
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Assigning one ansistring to another doesn't involve moving the actual
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string. A statement
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@@ -855,13 +866,14 @@ The referece count of \var{S1} is increased by one, and finally \var{S1}
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(as a pointer) is copied to \var{S2}. This is a significant speed-up in
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the code.
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-If a reference count reaches zero, then the memory occupied by the
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+If the reference count reaches zero, then the memory occupied by the
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string is deallocated automatically, so no memory leaks arise.
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When an ansistring is declared, the \fpc compiler initially
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allocates just memory for a pointer, not more. This pointer is guaranteed
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to be nil, meaning that the string is initially empty. This is
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-true for local, global or part of a structure (arrays, records or objects).
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+true for local and global ansistrings or anstrings that are part of a
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+structure (arrays, records or objects).
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This does introduce an overhead. For instance, declaring
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\begin{verbatim}
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@@ -869,12 +881,15 @@ Var
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A : Array[1..100000] of string;
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\end{verbatim}
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Will copy 100,000 times \var{nil} into \var{A}. When \var{A} goes out of scope, then
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-the 100,000 strings will be dereferenced one by one. All this happens
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+the reference count of the 100,000 strings will be decreased by 1 for each
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+of these strings. All this happens
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invisibly for the programmer, but when considering performance issues,
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this is important.
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Memory will be allocated only when the string is assigned a value.
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-If the string goes out of scope, then it is automatically dereferenced.
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+If the string goes out of scope, then its reference count is automatically
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+decreased by 1. If the reference count reaches zero, the memory reserved for
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+the string is released.
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If a value is assigned to a character of a string that has a reference count
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greater than 1, such as in the following
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@@ -922,6 +937,8 @@ It is therefore NOT advisable to typecast one of the following:
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\item strings that have reference count larger than 0.
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(call uniquestring to ensure a string has reference count 1)
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\end{enumerate}
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+
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+% Constant strings
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\subsection{Constant strings}
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To specify a constant string, it must be enclosed in single-quotes, just
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@@ -943,8 +960,8 @@ between them. Strings can not be substracted, however.
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Whether the constant string is stored as an ansistring or a short string
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depends on the settings of the \var{\{\$H\}} switch.
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-
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-\subsection{PChar}
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+% PChar
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+\subsection{PChar - Null terminated strings}
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\fpc supports the Delphi implementation of the \var{PChar} type. \var{PChar}
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is defined as a pointer to a \var{Char} type, but allows additional
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operations.
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@@ -3124,7 +3141,7 @@ Because of this, the calling block must pass a parameter of {\em exactly}
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the same type as the declared parameter's type. If it does not, the compiler
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will generate an error.
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-Variable parameters can be untyped. In that case the variable has no type,
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+Variable and constant parameters can be untyped. In that case the variable has no type,
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and hence is incompatible with all other types. However, the address operator
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can be used on it, or it can be can passed to a function that has also an
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untyped parameter. If an untyped parameter is used in an assigment,
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@@ -4929,6 +4946,7 @@ Functions concerning memory issues.
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\procref{New}{Dynamically allocate memory for variable}
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\funcref{Ofs}{Return offset of variable}
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\funcref{Ptr}{Combine segment and offset to pointer}
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+\funcref{ReAllocMem}{Resize a memory block on the heap}
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\procref{Release}{Release memory above mark point}
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\funcref{Seg}{Return segment}
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\procref{SetMemoryManager}{Set a memory manager}
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@@ -7512,6 +7530,25 @@ In case \var{Param} is an invalid value, an empty string is returned.
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For an example, see \seef{Paramstr}.
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+\begin{function}{ReAllocMem}
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+\Declaration
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+function ReAllocMem(var p:pointer;Size:Longint):pointer;
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+\Description
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+\var{ReAllocMem} resizes the memory pointed to by \var{P} so it has size
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+\var{Size}. The value of \var{P} may change during this operation.
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+The contents of the memory pointed to by \var{P} (if any) will be copied to
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+the new location, but may be truncated if the newly allocated memory block
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+is smaller in size. If a larger block is allocated, only the used memory is
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+initialized, extra memory will not be zeroed out.
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+
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+Note that \var{P} may be nil, in that case the behaviour of \var{ReAllocMem}
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+is equivalent to \seep{Getmem}.
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+\Errors
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+If no memory is available then a run-time error will occur.
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+\SeeAlso
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+\seep{Getmem}, \seep{Freemem}
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+\end{function}
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+
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\begin{procedure}{ResetResourceTables}
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\Declaration
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Procedure ResetResourceTables;
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michael