The manual for this Tcl C API function is at [L1 ].

Usage example

A simple Tcl code snippet to produce a random integer from 0 to 255 is:

return [expr {int(rand()*(255+1))}]

The C function Tcl_ExprLongObj can be used to code this in C like this (assuming this is called from a Tcl interpreter 'interp'):

Tcl_Obj *exprPtr;   /* pointer to hold the expression we want to evaluate */
long myresult;      /* the integer holding the result of the expression */
exprPtr = Tcl_NewStringObj("int(rand()*255+1)",-1); /* this prepares the expression, which must be given as a Tcl_Obj */
/* now evaluate the expression in exprPtr and put the result into myresult */
if (Tcl_ExprLongObj(interp,exprPtr,&myresult) != TCL_OK) {
    return TCL_ERROR;

DGP Perhaps worth noting that because Tcl_ExprLongObj() writes its result to a variable of type long, it implicitly performs the int(.) function as part of its nature. There's no need to include the int(.) call in the expression string.

Similar functions are Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, and Tcl_ExprObj.