Control Tcl memory debugging capabilities 

Tclsh Built-In Commands


memory option ?arg arg ...?


The memory command gives the Tcl developer control of Tcl's memory debugging capabilities. The memory command has several suboptions, which are described below. It is only available when Tcl has been compiled with memory debugging enabled (when TCL_MEM_DEBUG() is defined at compile time).

memory info 

Produces a report containing the total allocations and frees since Tcl began, the current packets allocated (the current number of calls to ckalloc not met by a corresponding call to ckfree), the current bytes allocated, and the maximum number of packets and bytes allocated.

memory trace [on|off] 

Turns memory tracing on or off. When memory tracing is on, every call to ckalloc causes a line of trace information to be written to stderr, consisting of the word ckalloc, followed by the address returned, the amount of memory allocated, and the C filename and line number of the code performing the allocation. For example:

ckalloc 40e478 98 tclProc.c 1406

Calls to ckfree are traced in the same manner.

memory validate [on|off] 

Turns memory validation on or off. When memory validation is enabled, on every call to ckalloc or ckfree, the guard zones are checked for every piece of memory currently in existence that was allocated by ckalloc. This has a large performance impact and should only be used when overwrite problems are strongly suspected. The advantage of enabling memory validation is that a guard zone overwrite can be detected on the first call to ckalloc or ckfree after the overwrite occurred, rather than when the specific memory with the overwritten guard zone(s) is freed, which may occur long after the overwrite occurred.

memory trace_on_at_malloc count 

Enable memory tracing after count ckalloc's have been performed. For example, if you enter memory trace_on_at_malloc 100, after the 100th call to ckalloc, memory trace information will begin being displayed for all allocations and frees. Since there can be a lot of memory activity before a problem occurs, judicious use of this option can reduce the slowdown caused by tracing (and the amount of trace information produced), if you can identify a number of allocations that occur before the problem sets in. The current number of memory allocations that have occurred since Tcl started is printed on a guard zone failure.

memory break_on_malloc count 

After the count allocations have been performed, ckalloc's output a message to this effect and that it is now attempting to enter the C debugger. Tcl will then issue a SIGINT signal against itself. If you are running Tcl under a C debugger, it should then enter the debugger command mode.

memory display file 

Write a list of all currently allocated memory to the specified file.


Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019. Windows 11. Windows Server 2022.


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Tcl_DumpActiveMemory(), TCL_MEM_DEBUG(), Tcl_ValidateAllMemory()

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