Tcl_AddObjErrorInfo(), Tcl_AddErrorInfo(), Tcl_SetObjErrorCode(), Tcl_SetErrorCode(), Tcl_SetErrorCodeVA(), Tcl_PosixError(), Tcl_LogCommandInfo()

record information about errors 

Tcl Library Procedures


SYNOPSIS

#include <tcl.h>

Tcl_AddObjErrorInfo(interp, message, length)

Tcl_AddErrorInfo(interp, message)

Tcl_SetObjErrorCode(interp, errorObjPtr)

Tcl_SetErrorCode(interp, element, element, ... (char *) NULL)

Tcl_SetErrorCodeVA(interp, argList)

char * Tcl_PosixError(interp)

void Tcl_LogCommandInfo(interp, script, command, commandLength)


ARGUMENTS

Tcl_Interp *interp (in) 

Interpreter in which to record information.

char *message (in) 

For Tcl_AddObjErrorInfo(), this points to the first byte of an array of bytes containing a string to record in the errorInfo variable. This byte array may contain embedded null bytes unless length is negative. For Tcl_AddErrorInfo(), this is a conventional C string to record in the errorInfo variable.

int length (in) 

The number of bytes to copy from message when setting the errorInfo variable. If negative, all bytes up to the first null byte are used.

Tcl_Obj *errorObjPtr (in) 

This variable errorCode will be set to this value.

char *element (in) 

String to record as one element of errorCode variable. Last element argument must be NULL.

va_list argList (in) 

An argument list which must have been initialized using TCL_VARARGS_START, and cleared using va_end.

char *script (in) 

Pointer to first character in script containing command (must be <= command)

char *command (in) 

Pointer to first character in command that generated the error

int commandLength (in) 

Number of bytes in command; -1 means use all bytes up to first NULL byte


DESCRIPTION

These procedures are used to manipulate two Tcl global variables that hold information about errors. The variable errorInfo holds a stack trace of the operations that were in progress when an error occurred, and is intended to be human-readable. The variable errorCode holds a list of items that are intended to be machine-readable. The first item in errorCode identifies the class of error that occurred (for example, POSIX means an error occurred in a POSIX system call) and additional elements in errorCode hold additional pieces of information that depend on the class. See the Tcl reference page for details on the various formats for errorCode.

The errorInfo variable is gradually built up as an error unwinds through the nested operations. Each time an error code is returned to Tcl_EvalObjEx() (or Tcl_Eval(), which calls Tcl_EvalObjEx()) it calls the procedure Tcl_AddObjErrorInfo() to add additional text to errorInfo describing the command that was being executed when the error occurred. By the time the error has been passed all the way back to the application, it will contain a complete trace of the activity in progress when the error occurred.

It is sometimes useful to add additional information to errorInfo beyond what can be supplied automatically by Tcl_EvalObjEx(). Tcl_AddObjErrorInfo() may be used for this purpose: its message and length arguments describe an additional string to be appended to errorInfo. For example, the source command calls Tcl_AddObjErrorInfo() to record the name of the file being processed and the line number on which the error occurred; for Tcl procedures, the procedure name and line number within the procedure are recorded, and so on. The best time to call Tcl_AddObjErrorInfo() is just after Tcl_EvalObjEx() has returned TCL_ERROR. In calling Tcl_AddObjErrorInfo(), you may find it useful to use the errorLine field of the interpreter (see the Tcl_Interp() reference page for details).

Tcl_AddErrorInfo() resembles Tcl_AddObjErrorInfo() but differs in initializing errorInfo from the string value of the interpreter's result if the error is just starting to be logged. It does not use the result as a Tcl object so any embedded null characters in the result will cause information to be lost. It also takes a conventional C string in message instead of Tcl_AddObjErrorInfo()'s counted string.

The procedure Tcl_SetObjErrorCode() is used to set the errorCode variable. errorObjPtr contains a list object built up by the caller. errorCode is set to this value. Tcl_SetObjErrorCode() is typically invoked just before returning an error in an object command. If an error is returned without calling Tcl_SetObjErrorCode() or Tcl_SetErrorCode() the Tcl interpreter automatically sets errorCode to NONE.

The procedure Tcl_SetErrorCode() is also used to set the errorCode variable. However, it takes one or more strings to record instead of an object. Otherwise, it is similar to Tcl_SetObjErrorCode() in behavior.

Tcl_SetErrorCodeVA() is the same as Tcl_SetErrorCode() except that instead of taking a variable number of arguments it takes an argument list.

Tcl_PosixError() sets the errorCode variable after an error in a POSIX kernel call. It reads the value of the errno C variable and calls Tcl_SetErrorCode() to set errorCode in the POSIX format. The caller must previously have called Tcl_SetErrno() to set errno; this is necessary on some platforms (for example, Windows) where Tcl is linked into an application as a shared library, or when the error occurs in a dynamically loaded extension. See the reference page for Tcl_SetErrno() for more information.

Tcl_PosixError() returns a human-readable diagnostic message for the error (this is the same value that will appear as the third element in errorCode). It may be convenient to include this string as part of the error message returned to the application in the interpreter's result.

Tcl_LogCommandInfo() is invoked after an error occurs in an interpreter. It adds information about the command that was being executed when the error occurred to the errorInfo variable, and the line number stored internally in the interpreter is set. On the first call to Tcl_LogCommandInfo() or Tcl_AddObjErrorInfo() since an error occurred, the old information in errorInfo is deleted.

It is important to call the procedures described here rather than setting errorInfo or errorCode directly with Tcl_ObjSetVar2(). The reason for this is that the Tcl interpreter keeps information about whether these procedures have been called. For example, the first time Tcl_AddObjErrorInfo() is called for an error, it clears the existing value of errorInfo and adds the error message in the interpreter's result to the variable before appending message; in subsequent calls, it just appends the new message. When Tcl_SetErrorCode() is called, it sets a flag indicating that errorCode has been set; this allows the Tcl interpreter to set errorCode to NONE if it receives an error return when Tcl_SetErrorCode() hasn't been called.

If the procedure Tcl_ResetResult() is called, it clears all of the state associated with errorInfo and errorCode (but it doesn't actually modify the variables). If an error had occurred, this will clear the error state to make it appear as if no error had occurred after all.


PORTABILITY

Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019. Windows 11. Windows Server 2022.


AVAILABILITY

PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition


SEE ALSO

Functions:
Tcl_DecrRefCount(), Tcl_IncrRefCount(), Tcl_Interp(), Tcl_ResetResult(), Tcl_SetErrno()


PTC MKS Toolkit 10.4 Documentation Build 39.