path: root/doc/Number.3

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.TH Tcl_GetNumber 3 8.7 Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_GetNumber, Tcl_GetNumberFromObj \- get numeric value from Tcl value
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
\fB#include <tclTomMath.h>\fR
.sp
int
\fBTcl_GetNumber\fR(\fIinterp, bytes, numBytes, clientDataPtr, typePtr\fR)
.sp
int
\fBTcl_GetNumberFromObj\fR(\fIinterp, objPtr, clientDataPtr, typePtr\fR)
.SH ARGUMENTS
.AS Tcl_Interp clientDataPtr out
.AP Tcl_Interp *interp out
When non-NULL, error information is recorded here when the value is not
in any of the numeric formats recognized by Tcl.
.AP "const char" *bytes in
Points to first byte of the string value to be examined.
.AP size_t numBytes in
The number of bytes, starting at \fIbytes\fR, that should be examined.
If the value \fBTCL_INDEX_NONE\fR is provided, then all bytes should
be examined until the first \fBNUL\fR byte terminates examination.
.AP "void *" *clientDataPtr out
Points to space where a pointer value may be written through which a numeric
value is available to read.
.AP int *typePtr out
Points to space where a value may be written reporting what type of
numeric storage is available to read.
.AP Tcl_Obj *objPtr in
A Tcl value to be examined.
.BE
.SH DESCRIPTION
.PP
These procedures enable callers to retrieve a numeric value from a
Tcl value in a numeric format recognized by Tcl.
.PP
Tcl recognizes many values as numbers.  Several examples include:
\fB"0"\fR, \fB" +1"\fR, \fB"-2 "\fR, \fB" 3 "\fR, \fB"0xdad1"\fR, \fB"0d09"\fR,
\fB"1_000_000"\fR, \fB"4.0"\fR, \fB"1e-7"\fR, \fB"NaN"\fR, or \fB"Inf"\fR.
When built-in Tcl commands act on these values as numbers, they are converted
to a numeric representation for efficient handling in C code.  Tcl makes
use of three C types to store these representations: \fBdouble\fR,
\fBTcl_WideInt\fR, and \fBmp_int\fR.  The \fBdouble\fR type is provided by the
C language standard.  The \fBTcl_WideInt\fR type is declared in the Tcl
header file, \fBtcl.h\fR, and is equivalent to the C standard type
\fBlong long\fR on most platforms. The \fBmp_int\fR type is declared in the
header file \fBtclTomMath.h\fR, and implemented by the LibTomMath
multiple-precision integer library, included with Tcl.
.PP
The routines \fBTcl_GetNumber\fR and \fBTcl_GetNumberFromObj\fR perform
the same function.  They differ only in how the arguments present the Tcl
value to be examined.  \fBTcl_GetNumber\fR accepts a counted string
value in the arguments \fIbytes\fR and \fInumBytes\fR (or a
\fBNUL\fR-terminated string value when \fInumBytes\fR is
\fBTCL_INDEX_NONE\fR).  \fBTcl_GetNumberFromObj\fR accepts the Tcl value
in \fIobjPtr\fR.
.PP
Both routines examine the Tcl value and determine whether Tcl recognizes
it as a number.  If not, both routines return \fBTCL_ERROR\fR and (when
\fIinterp\fR is not NULL) record an error message and error code
in \fIinterp\fR.
.PP
If Tcl does recognize the examined value as a number, both routines return
\fBTCL_OK\fR, and use the pointer arguments \fIclientDataPtr\fR
and \fItypePtr\fR (which may not be NULL) to report information the
caller can use to retrieve the numeric representation.  Both routines
write to *\fIclientDataPtr\fR a pointer to the internal storage location
where Tcl holds the converted numeric value.
.PP
When the converted numeric value is stored as a \fBdouble\fR,
a call to math library routine \fBisnan\fR determines whether that
value is not a number (NaN).  If so, both \fBTcl_GetNumber\fR and
\fBTcl_GetNumberFromObj\fR write the value \fBTCL_NUMBER_NAN\fR
to *\fItypePtr\fR. If not, both routines write the value
\fBTCL_NUMBER_DOUBLE\fR to *\fItypePtr\fR.  These routines report
different type values in these cases because \fBTcl_GetDoubleFromObj\fR
raises an error on NaN values.  For both reported type values,
the storage pointer may be cast to type \fBconst double *\fR and
the \fBdouble\fR numeric value may be read through it.
.PP
When the converted numeric value is stored as a \fBTcl_WideInt\fR,
both \fBTcl_GetNumber\fR and \fBTcl_GetNumberFromObj\fR write the
value \fBTCL_NUMBER_INT\fR to *\fItypePtr\fR.
The storage pointer may be cast to type \fBconst Tcl_WideInt *\fR and
the \fBTcl_WideInt\fR numeric value may be read through it.
.PP
When the converted numeric value is stored as an \fBmp_int\fR,
both \fBTcl_GetNumber\fR and \fBTcl_GetNumberFromObj\fR write the
value \fBTCL_NUMBER_BIG\fR to *\fItypePtr\fR.
The storage pointer may be cast to type \fBconst mp_int *\fR and
the \fBmp_int\fR numeric value may be read through it.
.PP
Future releases of Tcl might expand or revise the recognition of
values as numbers.  If additional storage representations are
adopted, these routines will add new values to be written to
*\fItypePtr\fR to identify them.  Callers should consider how
they should react to unknown values written to *\fItypePtr\fR.
.PP
When callers of these routines read numeric values through the
reported storage pointer, they are accessing memory that belongs
to the Tcl library.  The Tcl library has the power to overwrite
or free this memory.  The storage pointer reported by a call to
\fBTcl_GetNumber\fR or \fBTcl_GetNumberFromObj\fR should not be
used after the same thread has possibly returned control to the
Tcl library.  If longer term access to the numeric value is needed,
it should be copied into memory controlled by the caller.  Callers
must not attempt to write through or free the storage pointer.
.SH "SEE ALSO"
Tcl_GetDouble, Tcl_GetDoubleFromObj, Tcl_GetWideIntFromObj
.SH KEYWORDS
double, double value, double type, integer, integer value, integer type,
internal representation, value, value type, string representation