int Tcl_GetInt(interp, src, intPtr)
int Tcl_GetDouble(interp, src, doublePtr)
int Tcl_GetBoolean(interp, src, boolPtr)
These procedures convert from strings to integers or double-precision floating-point values or booleans (represented as 0- or 1-valued integers). Each of the procedures takes a src argument, converts it to an internal form of a particular type, and stores the converted value at the location indicated by the procedure's third argument. If all goes well, each of the procedures returns TCL_OK. If src does not have the proper syntax for the desired type then TCL_ERROR is returned, an error message is left in the interpreter's result, and nothing is stored at *intPtr or *doublePtr or *boolPtr.
Tcl_GetInt expects src to consist of a collection of integer digits, optionally signed and optionally preceded by white space. If the first two characters of src after the optional white space and sign are “0x” then src is expected to be in hexadecimal form; otherwise, if the first such character is “0” then src is expected to be in octal form; otherwise, src is expected to be in decimal form.
Tcl_GetDouble expects src to consist of a floating-point number, which is: white space; a sign; a sequence of digits; a decimal point; a sequence of digits; the letter “e” a signed decimal exponent; and more white space. Any of the fields may be omitted, except that the digits either before or after the decimal point must be present and if the “e” is present then it must be followed by the exponent number.
Tcl_GetBoolean expects src to specify a boolean value. If src is any of 0, false, no, or off, then Tcl_GetBoolean stores a zero value at *boolPtr. If src is any of 1, true, yes, or on, then 1 is stored at *boolPtr. Any of these values may be abbreviated, and upper-case spellings are also acceptable.