Tcl_ExprLong(3) Tcl Library Procedures Tcl_ExprLong(3)______________________________________________________________________________NAME
Tcl_ExprLong, Tcl_ExprDouble, Tcl_ExprBoolean, Tcl_ExprString - evalu‐
ate an expression
Tcl_ExprLong(interp, string, longPtr)
Tcl_ExprDouble(interp, string, doublePtr)
Tcl_ExprBoolean(interp, string, booleanPtr)
Tcl_Interp *interp (in) Interpreter in whose context to
evaluate string. │
CONST char *string (in) │
Expression to be evaluated.
long *longPtr (out) Pointer to location in which to
store the integer value of the
int *doublePtr (out) Pointer to location in which to
store the floating-point value of
int *booleanPtr (out) Pointer to location in which to
store the 0/1 boolean value of the
These four procedures all evaluate the expression given by the string
argument and return the result in one of four different forms. The
expression can have any of the forms accepted by the expr command.
Note that these procedures have been largely replaced by the object-
based procedures Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_Expr‐
BooleanObj, and Tcl_ExprObj. Those object-based procedures evaluate an
expression held in a Tcl object instead of a string. The object argu‐
ment can retain an internal representation that is more efficient to
The interp argument refers to an interpreter used to evaluate the
expression (e.g. for variables and nested Tcl commands) and to return
For all of these procedures the return value is a standard Tcl result:
TCL_OK means the expression was successfully evaluated, and TCL_ERROR
means that an error occurred while evaluating the expression. If
TCL_ERROR is returned then the interpreter's result will hold a message
describing the error. If an error occurs while executing a Tcl command
embedded in the expression then that error will be returned.
If the expression is successfully evaluated, then its value is returned
in one of four forms, depending on which procedure is invoked.
Tcl_ExprLong stores an integer value at *longPtr. If the expression's
actual value is a floating-point number, then it is truncated to an
integer. If the expression's actual value is a non-numeric string then
an error is returned.
Tcl_ExprDouble stores a floating-point value at *doublePtr. If the
expression's actual value is an integer, it is converted to floating-
point. If the expression's actual value is a non-numeric string then
an error is returned.
Tcl_ExprBoolean stores a 0/1 integer value at *booleanPtr. If the
expression's actual value is an integer or floating-point number, then
they store 0 at *booleanPtr if the value was zero and 1 otherwise. If
the expression's actual value is a non-numeric string then it must be
one of the values accepted by Tcl_GetBoolean such as ``yes'' or ``no'',
or else an error occurs.
Tcl_ExprString returns the value of the expression as a string stored
in the interpreter's result.
Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, Tcl_ExprObj
boolean, double, evaluate, expression, integer, object, string
Tcl 7.0 Tcl_ExprLong(3)