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 term_variables(3X).

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 that 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 sent to the terminal device with tputs or putp. Call reset_shell_mode to restore the terminal modes before exiting; see curs_kernel(3X).

Programs that use cursor addressing should

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

Programs that 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.

setupterm reads in the terminfo database, initializing the terminfo structures, but does not set up the output virtualization structures used by curses. Its parameters follow.

The Terminal State

setupterm 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.

set_curterm 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.

del_curterm 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.

restartterm 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 terminal state bits, calls setupterm, and then restores the bits.

Formatting Output

tparm 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 ints rather than longs.

Both tparm and tiparm assume that the application passes parameters consistent with the terminal description. Two extensions are provided as alternatives to deal with untrusted data.

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tiparm_s is an extension which is a safer formatting function than tparm or tiparm, because it allows the developer to tell the curses library how many parameters to expect in the parameter list, and which may be string parameters.

The mask parameter has one bit set for each of the parameters (up to 9) passed as char pointers rather than numbers.

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The extension tiscan_s allows the application to inspect a formatting capability to see what the curses library would assume.

Output Functions

String capabilities can contain padding information, a time delay (accommodating performance limitations of hardware terminals) expressed as $<n>, where n is a nonnegative integral count of milliseconds. If n exceeds 30,000 (thirty seconds), it is capped at that value.

tputs interprets time-delay information in the string str and outputs it, executing the delays:

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

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

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

If tputs processes a time-delay, it uses the delay_output(3X) function, routing any resulting padding characters through this function.

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

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

vidattr is like vidputs, except that it outputs through putchar(3).

vid_attr and vid_puts correspond to vidattr and vidputs, respectively. They use multiple parameters to represent the character attributes and color; namely,

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

Use the attribute constants prefixed with “WA_” with vid_attr and vid_puts.

X/Open Curses reserves the opts argument for future use, saying that applications must provide a null pointer for that argument; but see section “EXTENSIONS” below.

mvcur provides low-level cursor motion. It takes effect immediately (rather than at the next refresh). Unlike the other low-level output functions, which either write to the standard output or pass an output function parameter, mvcur uses an output file descriptor derived from the output stream parameter of newterm(3X).

While putp and mvcur are low-level functions that do not use high-level curses state, ncurses declares them in curses.h because System V did this (see section “HISTORY” below).

Terminal Capability Functions

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

These functions return special values to denote errors.

tigetflag returns

-1

if cap-code is not a Boolean capability, or

0

if it is canceled or absent from the terminal description.

tigetnum returns

-2

if cap-code is not a numeric capability, or

-1

if it is canceled or absent from the terminal description.

tigetstr returns

(char *)-1

if cap-code 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:

const char *boolnames[], *boolcodes[], *boolfnames[]
const char *numnames[], *numcodes[], *numfnames[]
const char *strnames[], *strcodes[], *strfnames[]

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 as follows.

• They add 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).
• 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 section “HISTORY” below). They include Bcrmode, Bfixterm, Bgettmode, Bnocrmode, Bresetterm, Bsaveterm, and Bsetterm.

In SVr4, these are found in curses.h, but except for setterm, are likewise macros. The one function, setterm, is mentioned in the manual page. It further notes that setterm was replaced by setupterm, stating that the call

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

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 Curses does not specify them.

Extended terminal capability names, as defined by “gtic -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 clean up 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 employ 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.

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X/Open Curses uses const less effectively than a later design might, sometimes applying it needlessly to values that are already constant, and in most cases overlooking parameters that normally would use const. Passing const-qualified parameters to functions that do not declare them 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.

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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 nine 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.

While tiparm is always provided in ncurses, the older form is only available as a build-time configuration option. If not specially configured, tparm is the same as tiparm.

Both forms of tparm have drawbacks:

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Most of the calls to tparm use only one or two parameters. Passing nine on each call is awkward.

Using long for the numeric parameter type is a workaround to make the parameter use the same amount of stack as a pointer. That approach dates back to the mid-1980s, before C was standardized. Since then, there is a standard (and pointers are not required to fit in a long).

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Providing the right number of parameters for a variadic function such as tiparm can be a problem, in particular for string parameters. However, only a few terminfo capabilities use string parameters (for instance, the ones used for programmable function keys).

The ncurses library checks usage of these capabilities, and returns an error if the capability mishandles string parameters. But it cannot check if a calling program provides strings in the right places for the tparm calls.

The gtput(1) program checks its use of these capabilities with a table, so that it calls tparm correctly.

Special TERM treatment

If configured to use the terminal driver, as with the MinGW port,

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setupterm interprets a missing/empty TERM variable as the special value “unknown”.

SVr4 curses uses the special value “dumb”.

The difference between the two is that the former uses the generic_type (gn) terminfo capability, while the latter does not. A generic terminal is unsuitable for full-screen applications.

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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 SVr4, set_curterm returns an int, OK or ERR. We have chosen to implement the X/Open Curses semantics.

In SVr4, 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 or ERR from tputs. It instead returns the length of the string, and does no error checking.

X/Open Curses 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 SVr4 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 that is not well specified.

X/Open Curses states that the old location must be given for mvcur to accommodate terminals that lack absolute cursor positioning. ncurses allows the caller to use -1 for either or both old coordinates. The -1 tells ncurses that the old location is unknown, and that it must use only absolute motion, as with the cursor_address (cup) capability, rather than the least costly combination of absolute and relative motion.