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Blt_TreeCreate(3) BLT Library Procedures Blt_TreeCreate(3)


Blt_TreeCreate - Create tree data object.


#include <bltTree.h>

Blt_TreeCreate(interp, name, tokenPtr)


Tcl_Interp *interp (in)
Interpreter to report results back to.
const char *name (in)
Name of the new tree. Can be qualified by a namespace.
Blt_Tree *tokenPtr (out)
If not NULL, points to location to store the client tree token.


This procedure creates a C-based tree data object and optionally returns a token to it. The arguments are as follows:

Interpreter to report results back to. If an error occurs, then interp->result will contain an error message.
Name of the new tree object. You can think of name as the memory address of the object. It's a unique name that identifies the tree object. No tree object name can already exist. Name can be qualified by a namespace such as fred::myTree. If no namespace qualifier is used, the tree will be created in the current namespace, not the global namespace. If a qualifier is present, the namespace must already exist.
Holds the returned token. TokenPtr points to a location where it is stored. Tree tokens are used to work with the tree object. If NULL, no token is allocated. You can later use Tcl_TreeGetToken to obtain a token.

The new tree data object created will initially contain only a root node. You can add new nodes with Blt_TreeCreateNode.

Optionally a token for the tree data object is returned. Tree data objects can be shared. For example, the tree and hiertable commands may be accessing the same tree data object. Each client grabs a token that is associated with the tree. When all tokens are released (see Blt_TreeReleaseToken) the tree data object is automatically destroyed.


A standard Tcl result is returned. If TCL_ERROR is returned, then interp->result will contain an error message. The following errors may occur:

  • There already exists a tree by the same name as name. You can use Tcl_TreeExists to determine if a tree exists beforehand.
  • The tree name is prefixed by a namespace that doesn't exist. If you qualified the tree name with a namespace, the namespace must exist. Unlike Tcl procs and variables, the namespace is not automatically created for you.
  • Memory can't be allocated for the tree or token.


The following example creates a new

Blt_Tree token;
if (Blt_TreeCreate(interp, "myTree", &token) != TCL_OK) {

return TCL_ERROR; } printf("tree is %s\n", Blt_TreeName(token));


Tcl_TreeGetToken, Tcl_TreeExists, Tcl_TreeReleaseToken

2.5 BLT