Tcl 9.0/Tk9.0 Documentation > Tcl C API, version 9.0.0 > WrongNumArgs

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NAME

Tcl_WrongNumArgs — generate standard error message for wrong number of arguments

SYNOPSIS

#include <tcl.h>
Tcl_WrongNumArgs(interp, objc, objv, message)

ARGUMENTS

Tcl_Interp interp (in)

Interpreter in which error will be reported: error message gets stored in its result value.

Tcl_Size objc (in)

Number of leading arguments from objv to include in error message.

Tcl_Obj *const objv[] (in)

Arguments to command that had the wrong number of arguments.

const char *message (in)

Additional error information to print after leading arguments from objv. This typically gives the acceptable syntax of the command. This argument may be NULL.

DESCRIPTION

Tcl_WrongNumArgs is a utility procedure that is invoked by command procedures when they discover that they have received the wrong number of arguments. Tcl_WrongNumArgs generates a standard error message and stores it in the result value of interp. The message includes the objc initial elements of objv plus message. For example, if objv consists of the values foo and bar, objc is 1, and message is “fileName count” then interp's result value will be set to the following string:

wrong # args: should be "foo fileName count"

If objc is 2, the result will be set to the following string:

wrong # args: should be "foo bar fileName count"

Objc is usually 1, but may be 2 or more for commands like string and the Tk widget commands, which use the first argument as a subcommand.

Some of the values in the objv array may be abbreviations for a subcommand. The command Tcl_GetIndexFromObj will convert the abbreviated string value into an indexObject. If an error occurs in the parsing of the subcommand we would like to use the full subcommand name rather than the abbreviation. If the Tcl_WrongNumArgs command finds any indexObjects in the objv array, it will use the full subcommand name in the error message instead of the abbreviated name that was originally passed in. Using the above example, let us assume that bar is actually an abbreviation for barfly and the value is now an indexObject because it was passed to Tcl_GetIndexFromObj. In this case the error message would be:

wrong # args: should be "foo barfly fileName count"

REFERENCE COUNT MANAGEMENT

The objv argument to Tcl_WrongNumArgs should be the exact arguments passed to the command or method implementation function that is calling Tcl_WrongNumArgs. As such, all values referenced in it should have reference counts greater than zero; this is usually a non-issue.

SEE ALSO

Tcl_GetIndexFromObj

KEYWORDS

command, error message, wrong number of arguments