On UNIX platforms, the function should be passed argv[0] as its argument. It is important not to change the working directory before this invocation. Tcl_FindExecutable uses argv0 together with the PATH environment variable to locate the application's executable, if possible. If it fails to find the binary, subsequent calls to info nameofexecutable will return an empty string.
On Windows platforms, the argv[0] argument is used only to indicate whether the executable has a standard error channel (any non-null value) or not (the value null). If Tcl_SetPanicProc is never called and no debugger is running, this setting determines whether a panic message is sent to standard error or displayed in a system dialog.
As part of its initialization sequence, Tcl_FindExecutable computes the full path name of the executable file from which the application was invoked. This result is saved for Tcl's internal use and is returned by the info nameofexecutable command.
The result of Tcl_FindExecutable is the full Tcl version string, including build information (for example, 9.0.0+abcdef...abcdef.gcc-1002).
Tcl_GetNameOfExecutable simply returns a pointer to the internal full path name of the executable file as computed by Tcl_FindExecutable. This procedure call is the C API equivalent to the info nameofexecutable command. NULL is returned if the internal full path name has not been computed or unknown.
Tcl_FindExecutable can not be used in stub-enabled extensions.