Initialization¶

Initially, setupterm should be called. The high-level curses functions initscr and newterm call setupterm to initialize the low-level set of terminal-dependent variables [listed in terminfo(5)].

Applications can use the terminal capabilities either directly (via header definitions), or by special functions. The header files curses.h and term.h should be included (in this order) to get the definitions for these strings, numbers, and flags.

The terminfo variables lines and columns are initialized by setupterm as follows:

• If use_env(FALSE) has been called, values for lines and columns specified in terminfo are used.
• Otherwise, if the environment variables LINES and COLUMNS exist, their values are used. If these environment variables do not exist and the program is running in a window, the current window size is used. Otherwise, if the environment variables do not exist, the values for lines and columns specified in the terminfo database are used.

Parameterized strings should be passed through tparm to instantiate them. All terminfo strings (including the output of tparm) should be printed with tputs or putp. Call reset_shell_mode to restore the tty modes before exiting [see kernel(3NCURSES)].

Programs which use cursor addressing should

• output enter_ca_mode upon startup and
• output exit_ca_mode before exiting.

Programs which execute shell subprocesses should

• call reset_shell_mode and output exit_ca_mode before the shell is called and
• output enter_ca_mode and call reset_prog_mode after returning from the shell.

The setupterm routine reads in the terminfo database, initializing the terminfo structures, but does not set up the output virtualization structures used by curses. These are its parameters:

The Terminal State¶

The setupterm routine stores its information about the terminal in a TERMINAL structure pointed to by the global variable cur_term. If it detects an error, or decides that the terminal is unsuitable (hardcopy or generic), it discards this information, making it not available to applications.

If setupterm is called repeatedly for the same terminal type, it will reuse the information. It maintains only one copy of a given terminal's capabilities in memory. If it is called for different terminal types, setupterm allocates new storage for each set of terminal capabilities.

The set_curterm routine sets cur_term to nterm, and makes all of the terminfo boolean, numeric, and string variables use the values from nterm. It returns the old value of cur_term.

The del_curterm routine frees the space pointed to by oterm and makes it available for further use. If oterm is the same as cur_term, references to any of the terminfo boolean, numeric, and string variables thereafter may refer to invalid memory locations until another setupterm has been called.

The restartterm routine is similar to setupterm and initscr, except that it is called after restoring memory to a previous state (for example, when reloading a game saved as a core image dump). restartterm assumes that the windows and the input and output options are the same as when memory was saved, but the terminal type and baud rate may be different. Accordingly, restartterm saves various tty state bits, calls setupterm, and then restores the bits.

Formatting Output¶

The tparm routine instantiates the string str with parameters pi. A pointer is returned to the result of str with the parameters applied. Application developers should keep in mind these quirks of the interface:

• Although tparm's actual parameters may be integers or strings, the prototype expects long (integer) values.
• Aside from the set_attributes (sgr) capability, most terminal capabilities require no more than one or two parameters.
• Padding information is ignored by tparm; it is interpreted by tputs.
• The capability string is null-terminated. Use “\200” where an ASCII NUL is needed in the output.

tiparm is a newer form of tparm which uses <stdarg.h> rather than a fixed-parameter list. Its numeric parameters are integers (int) rather than longs.

Output Functions¶

The tputs routine applies padding information (i.e., by interpreting marker embedded in the terminfo capability such as “$<5>” as 5 milliseconds) to the string str and outputs it:

•

The str parameter must be a terminfo string variable or the return value from tparm, tiparm, tgetstr, or tgoto.

The tgetstr and tgoto functions are part of the termcap interface, which happens to share this function name with the terminfo interface.

• affcnt is the number of lines affected, or 1 if not applicable.
• putc is a putchar-like routine to which the characters are passed, one at a time.

The putp routine calls tputs(str, 1, putchar). The output of putp always goes to stdout, rather than the filedes specified in setupterm.

The vidputs routine displays the string on the terminal in the video attribute mode attrs, which is any combination of the attributes listed in ncurses(3NCURSES). The characters are passed to the putchar-like routine putc.

The vidattr routine is like the vidputs routine, except that it outputs through putchar.

The vid_attr and vid_puts routines correspond to vidattr and vidputs, respectively. They use a set of arguments for representing the video attributes plus color, i.e.,

• attrs of type attr_t for the attributes and
• pair of type short for the color-pair number.

The vid_attr and vid_puts routines are designed to use the attribute constants with the WA_ prefix.

X/Open Curses reserves the opts argument for future use, saying that applications must provide a null pointer for that argument. As an extension, this implementation allows opts to be used as a pointer to int, which overrides the pair (short) argument.

The mvcur routine provides low-level cursor motion. It takes effect immediately (rather than at the next refresh).

While putp and mvcur are low-level functions which do not use the high-level curses state, they are declared in <curses.h> because SystemV did this (see HISTORY).

Terminal Capability Functions¶

The tigetflag, tigetnum and tigetstr routines return the value of the capability corresponding to the terminfo capname passed to them, such as xenl. The capname for each capability is given in the table column entitled capname code in the capabilities section of terminfo(5).

These routines return special values to denote errors.

The tigetflag routine returns

-1

if capname is not a boolean capability, or

0

if it is canceled or absent from the terminal description.

The tigetnum routine returns

-2

if capname is not a numeric capability, or

-1

if it is canceled or absent from the terminal description.

The tigetstr routine returns

(char *)-1

if capname is not a string capability, or

0

if it is canceled or absent from the terminal description.

Terminal Capability Names¶

These null-terminated arrays contain

• the short terminfo names (“codes”),
• the termcap names (“names”), and
• the long terminfo names (“fnames”)

for each of the predefined terminfo variables:

Releasing Memory¶

Each successful call to setupterm allocates memory to hold the terminal description. As a side-effect, it sets cur_term to point to this memory. If an application calls

del_curterm(cur_term);

the memory will be freed.

The formatting functions tparm and tiparm extend the storage allocated by setupterm:

• the “static” terminfo variables [a-z]. Before ncurses 6.3, those were shared by all screens. With ncurses 6.3, those are allocated per screen. See terminfo(5) for details.
• to improve performance, ncurses 6.3 caches the result of analyzing terminfo strings for their parameter types. That is stored as a binary tree referenced from the TERMINAL structure.

The higher-level initscr and newterm functions use setupterm. Normally they do not free this memory, but it is possible to do that using the delscreen(3X) function.

Compatibility macros¶

This implementation provides a few macros for compatibility with systems before SVr4 (see HISTORY). Those include crmode, fixterm, gettmode, nocrmode, resetterm, saveterm, and setterm.

In SVr4, those are found in <curses.h>, but except for setterm, are likewise macros. The one function, setterm, is mentioned in the manual page. The manual page notes that the setterm routine was replaced by setupterm, stating that the call:

setupterm(term, 1, (int *)0)

provides the same functionality as setterm(term), and is not recommended for new programs. This implementation provides each of those symbols as macros for BSD compatibility,

Legacy functions¶

X/Open notes that vidattr and vidputs may be macros.

The function setterm is not described by X/Open and must be considered non-portable. All other functions are as described by X/Open.

Legacy data¶

setupterm copies the terminal name to the array ttytype. This is not part of X/Open Curses, but is assumed by some applications.

Other implementions may not declare the capability name arrays. Some provide them without declaring them. X/Open does not specify them.

Extended terminal capability names, e.g., as defined by tic -x, are not stored in the arrays described here.

Output buffering¶

Older versions of ncurses assumed that the file descriptor passed to setupterm from initscr or newterm uses buffered I/O, and would write to the corresponding stream. In addition to the limitation that the terminal was left in block-buffered mode on exit (like System V curses), it was problematic because ncurses did not allow a reliable way to cleanup on receiving SIGTSTP.

The current version (ncurses6) uses output buffers managed directly by ncurses. Some of the low-level functions described in this manual page write to the standard output. They are not signal-safe. The high-level functions in ncurses use alternate versions of these functions using the more reliable buffering scheme.

Function prototypes¶

The X/Open Curses prototypes are based on the SVr4 curses header declarations, which were defined at the same time the C language was first standardized in the late 1980s.

•

X/Open Curses uses const less effectively than a later design might, in some cases applying it needlessly to values are already constant, and in most cases overlooking parameters which normally would use const. Using constant parameters for functions which do not use const may prevent the program from compiling. On the other hand, writable strings are an obsolescent feature.

As an extension, this implementation can be configured to change the function prototypes to use the const keyword. The ncurses ABI 6 enables this feature by default.

•

X/Open Curses prototypes tparm with a fixed number of parameters, rather than a variable argument list.

This implementation uses a variable argument list, but can be configured to use the fixed-parameter list. Portable applications should provide 9 parameters after the format; zeroes are fine for this purpose.

In response to review comments by Thomas E. Dickey, X/Open Curses Issue 7 proposed the tiparm function in mid-2009.

Special TERM treatment¶

If configured to use the terminal-driver, e.g., for the MinGW port,

• setupterm interprets a missing/empty TERM variable as the special value “unknown”.
• setupterm allows explicit use of the the windows console driver by checking if $TERM is set to “#win32con” or an abbreviation of that string.

Other portability issues¶

In System V Release 4, set_curterm has an int return type and returns OK or ERR. We have chosen to implement the X/Open Curses semantics.

In System V Release 4, the third argument of tputs has the type int (*putc)(char).

At least one implementation of X/Open Curses (Solaris) returns a value other than OK/ERR from tputs. That returns the length of the string, and does no error-checking.

X/Open notes that after calling mvcur, the curses state may not match the actual terminal state, and that an application should touch and refresh the window before resuming normal curses calls. Both ncurses and System V Release 4 curses implement mvcur using the SCREEN data allocated in either initscr or newterm. So though it is documented as a terminfo function, mvcur is really a curses function which is not well specified.

X/Open states that the old location must be given for mvcur. This implementation allows the caller to use -1's for the old ordinates. In that case, the old location is unknown.