Tcl_SetErrno man page

Tcl_SetErrno, Tcl_GetErrno, Tcl_ErrnoId, Tcl_ErrnoMsg — manipulate errno to store and retrieve error codes


#include <tcl.h>



const char *

const char *


int errorCode (in)
A POSIX error code such as ENOENT.


Tcl_SetErrno and Tcl_GetErrno provide portable access to the errno variable, which is used to record a POSIX error code after system calls and other operations such as Tcl_Gets. These procedures are necessary because global variable accesses cannot be made across module boundaries on some platforms.

Tcl_SetErrno sets the errno variable to the value of the errorCode argument C procedures that wish to return error information to their callers via errno should call Tcl_SetErrno rather than setting errno directly.

Tcl_GetErrno returns the current value of errno. Procedures wishing to access errno should call this procedure instead of accessing errno directly.

Tcl_ErrnoId and Tcl_ErrnoMsg return string representations of errno values. Tcl_ErrnoId returns a machine-readable textual identifier such as “EACCES” that corresponds to the current value of errno. Tcl_ErrnoMsg returns a human-readable string such as “permission denied” that corresponds to the value of its errorCode argument. The errorCode argument is typically the value returned by Tcl_GetErrno. The strings returned by these functions are statically allocated and the caller must not free or modify them.


errno, error code, global variables

Referenced By

Tcl_CreateChannel(3), Tcl_GetReturnOptions(3), Tcl_SetChannelError(3).

Tcl_ErrnoId(3), Tcl_ErrnoMsg(3) and Tcl_GetErrno(3) are aliases of Tcl_SetErrno(3).

8.3 Tcl Tcl Library Procedures