Initialization

Call setupterm from your application to have terminfo manage the terminal device; this action initializes the terminal-dependent variables listed in terminfo_variables(3NCURSES). (A curses application calling initscr(3NCURSES) or newterm(3NCURSES) achieves the same result.) Applications can use the terminal capabilities either directly, by object definitions corresponding to capability names and codes (see terminfo_variables(3NCURSES)) or by calling the functions documented here. setupterm initializes the terminfo variables lines and columns as described in use_env(3NCURSES).

Pass parameterized string capability values 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(3NCURSES) to restore the terminal modes before exiting. (A curses application calling endwin(3NCURSES) achieves the same result.)

Programs that use cursor addressing should emit certain capabilities at specific times. Specifically, output

• enter_ca_mode upon startup, and
• exit_ca_mode before exiting.

Programs that execute shell subprocesses should

• call reset_shell_mode(3NCURSES) and output exit_ca_mode before the shell is called, and
• output enter_ca_mode and call reset_prog_mode(3NCURSES) 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 unavailable to applications.

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

set_curterm sets cur_term to nterm, making all of the terminfo Boolean, numeric, and string capabilities use the values from nterm. It returns the old value of cur_term.

del_curterm frees the memory pointed to by oterm, making it available for further use. If oterm is the same as cur_term, references to any of the terminfo Boolean, numeric, and string capabilities thereafter may refer to invalid memory locations until setupterm is called again.

restartterm is similar to setupterm, but is intended for use after restoring program memory to a previous state (for example, when reloading an application that has been suspended from one terminal session and restored in another). restartterm assumes that the display dimensions and the input and output options are the same as when memory was saved, but the terminal type and line speed may differ. Accordingly, restartterm saves relevant terminal state, calls setupterm, then restores that state.

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, 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:

• The str parameter must be a terminfo string variable or the return value of tparm or tiparm.
• 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(3NCURSES) 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 ncurses(3NCURSES). 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.

While putp is a lower-level function that does not use higher-level curses state, ncurses declares it in curses.h because System V did so (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 of that name in the “Predefined 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

NULL

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 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(3NCURSES) function.

Header Files

On legacy curses systems, include curses.h and term.h in that order to make visible the definitions of the string arrays storing the capability names and codes.

Compatibility Macros

ncurses implements a few macros for early System V curses compatibility (see section “HISTORY” below). They include crmode, fixterm, gettmode, nocrmode, resetterm, saveterm, and setterm.

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)

setterm(term)

Legacy Data

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

Other implementations 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 “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 used buffered I/O, and wrote to the corresponding stdio 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.

ncurses 6.x uses output buffers managed directly by ncurses. The lower-level functions described here that write to the terminal device do so via the standard output stream; they thus are not signal-safe. The higher-level functions in ncurses employ alternate versions of these functions using a 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 benefit from 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 C language feature.

As an extension, ncurses 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.

ncurses 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 available only 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 calls to tparm require 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 memory as a pointer. That approach dates to the mid-1980s, before C was standardized. Since ANSI C (1989), C language standards do not require a pointer 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 ERR if the capability mishandles string parameters. But it cannot check if a calling program provides strings in the right places for the tparm calls.

ncurses's tput(1) checks its use of these capabilities with a table, so that it calls tparm correctly.

Special TERM treatment

If ncurses is 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 Microsoft Windows console driver by checking whether the TERM environment variable has the value “#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 (*)(char)”.

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