HPUX Interp[3]
Interp in anderen Kapiteln des hpux Handbuch:
Tcl_Interp(3) Tcl Tcl_Interp(3)
Tcl Library Procedures Tcl Library Procedures
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NAME
Tcl_Interp - client-visible fields of interpreter structures
SYNOPSIS
#include <tcl.h>
typedef struct {
char *result;
Tcl_FreeProc *freeProc;
int errorLine;
} Tcl_Interp;
typedef void Tcl_FreeProc(char *blockPtr);
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DESCRIPTION
The Tcl_CreateInterp procedure returns a pointer to a Tcl_Interp
structure. This pointer is then passed into other Tcl procedures to
process commands in the interpreter and perform other operations on
the interpreter. Interpreter structures contain many many fields that
are used by Tcl, but only three that may be accessed by clients:
result, freeProc, and errorLine.
The result and freeProc fields are used to return results or error
messages from commands. This information is returned by command
procedures back to Tcl_Eval, and by Tcl_Eval back to its callers. The
result field points to the string that represents the result or error
message, and the freeProc field tells how to dispose of the storage
for the string when it isn't needed anymore. The easiest way for
command procedures to manipulate these fields is to call procedures
like Tcl_SetResult or Tcl_AppendResult; they will hide all the
details of managing the fields. The description below is for those
procedures that manipulate the fields directly.
Whenever a command procedure returns, it must ensure that the result
field of its interpreter points to the string being returned by the
command. The result field must always point to a valid string. If a
command wishes to return no result then interp->result should point to
an empty string. Normally, results are assumed to be statically
allocated, which means that the contents will not change before the
next time Tcl_Eval is called or some other command procedure is
invoked. In this case, the freeProc field must be zero.
Alternatively, a command procedure may dynamically allocate its return
value (e.g. using malloc) and store a pointer to it in interp->result.
In this case, the command procedure must also set interp->freeProc to
the address of a procedure that can free the value (usually free). If
- 1 - Formatted: August 11, 1996
Tcl_Interp(3) Tcl Tcl_Interp(3)
Tcl Library Procedures Tcl Library Procedures
interp->freeProc is non-zero, then Tcl will call freeProc to free the
space pointed to by interp->result before it invokes the next command.
If a client procedure overwrites interp->result when interp->freeProc
is non-zero, then it is responsible for calling freeProc to free the
old interp->result (the Tcl_FreeResult macro should be used for this
purpose).
FreeProc should have arguments and result that match the Tcl_FreeProc
declaration above: it receives a single argument which is a pointer
to the result value to free. In most applications free is the only
non-zero value ever used for freeProc. However, an application may
store a different procedure address in freeProc in order to use an
alternate memory allocator or in order to do other cleanup when the
result memory is freed.
As part of processing each command, Tcl_Eval initializes interp-
>result and interp->freeProc just before calling the command procedure
for the command. The freeProc field will be initialized to zero, and
interp->result will point to an empty string. Commands that do not
return any value can simply leave the fields alone. Furthermore, the
empty string pointed to by result is actually part of an array of
TCL_RESULT_SIZE characters (approximately 200). If a command wishes
to return a short string, it can simply copy it to the area pointed to
by interp->result. Or, it can use the sprintf procedure to generate a
short result string at the location pointed to by interp->result.
It is a general convention in Tcl-based applications that the result
of an interpreter is normally in the initialized state described in
the previous paragraph. Procedures that manipulate an interpreter's
result (e.g. by returning an error) will generally assume that the
result has been initialized when the procedure is called. If such a
procedure is to be called after the result has been changed, then
Tcl_ResetResult should be called first to reset the result to its
initialized state.
The errorLine field is valid only after Tcl_Eval returns a TCL_ERROR
return code. In this situation the errorLine field identifies the
line number of the command being executed when the error occurred.
The line numbers are relative to the command being executed: 1 means
the first line of the command passed to Tcl_Eval, 2 means the second
line, and so on. The errorLine field is typically used in conjunction
with Tcl_AddErrorInfo to report information about where an error
occurred. ErrorLine should not normally be modified except by
Tcl_Eval.
KEYWORDS
free, initialized, interpreter, malloc, result
- 2 - Formatted: August 11, 1996