terminfo(3) | Library calls | terminfo(3)

# NAME

del_curterm, mvcur, putp, restartterm, set_curterm, setupterm, tigetflag, tigetnum, tigetstr, tiparm, tiparm_s, tiscan_s, tparm, tputs, vid_attr, vid_puts, vidattr, vidputs - curses interfaces to terminfo database

# SYNOPSIS

    #include <curses.h>
    #include <term.h>

    TERMINAL *cur_term;

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

    int setupterm(const char *term, int filedes, int *errret);

    TERMINAL *set_curterm(TERMINAL *nterm);

    int del_curterm(TERMINAL *oterm);

    int restartterm(const char *term, int filedes, int *errret);

    char *tparm(const char *str, ...);

    	or

    char *tparm(const char *str, long p1 ... long p9);

    int tputs(const char *str, int affcnt, int (*putc)(int));

    int putp(const char *str);

    int vidputs(chtype attrs, int (*putc)(int));

    int vidattr(chtype attrs);

    int vid_puts(attr_t attrs, short pair, void *opts, int (*putc)(int));

    int vid_attr(attr_t attrs, short pair, void *opts);

    int mvcur(int oldrow, int oldcol, int newrow, int newcol);

    int tigetflag(const char *capname);

    int tigetnum(const char *capname);

    char *tigetstr(const char *capname);

    char *tiparm(const char *str, ...);

    /* extensions */

    char *tiparm_s(int expected, int mask, const char *str, ...);

    int tiscan_s(int *expected, int *mask, const char *str);

# DESCRIPTION

These low-level routines must be called by programs that have to deal directly with the terminfo database to handle certain terminal capabilities, such as programming function keys. For all other functionality, curses routines are more suitable and their use is recommended.

None of these functions use (or are aware of) multibyte character strings such as UTF-8:

- capability names use the POSIX portable character set
- capability string values have no associated encoding; they are strings of 8-bit characters.

## 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 curs_kernel(3)].

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:

term
  is the terminal type, a character string. If term is null, the environment variable TERM is used.
filedes
  is the file descriptor used for getting and setting terminal I/O modes.

  Higher-level applications use newterm(3) for initializing the terminal, passing an output stream rather than a descriptor. In curses, the two are the same because newterm calls setupterm, passing the file descriptor derived from its output stream parameter.

errret
  points to an optional location where an error status can be returned to the caller. If errret is not null, then setupterm returns OK or ERR and stores a status value in the integer pointed to by errret. A return value of OK combined with status of 1 in errret is normal.

  If ERR is returned, examine errret:

1
  means that the terminal is hardcopy, cannot be used for curses applications.

  setupterm determines if the entry is a hardcopy type by checking the hc (hardcopy) capability.

0
  means that the terminal could not be found, or that it is a generic type, having too little information for curses applications to run.

  setupterm determines if the entry is a generic type by checking the gn (generic_type) capability.

-1
  means that the terminfo database could not be found.

  If errret is null, setupterm prints an error message upon finding an error and exits. Thus, the simplest call is:

  setupterm((char *)0, 1, (int *)0);,

  which uses all the defaults and sends the output to stdout.

## 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.

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:

•
  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) which will be passed as char* rather than numbers.

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

## 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 curses(3). 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). 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(3).

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:

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:

- 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(3) function.

# RETURN VALUE

Routines that return an integer return ERR upon failure and OK (SVr4 only specifies “an integer value other than ERR”) upon successful completion, unless otherwise noted in the preceding routine descriptions.

Routines that return pointers always return NULL on error.

X/Open defines no error conditions. In this implementation

del_curterm
  returns an error if its terminal parameter is null.
putp
  calls tputs, returning the same error-codes.
restartterm
  returns an error if the associated call to setupterm returns an error.
setupterm
  returns an error if it cannot allocate enough memory, or create the initial windows (stdscr, curscr, newscr). Other error conditions are documented above.
tparm
  returns a null if the capability would require unexpected parameters, e.g., too many, too few, or incorrect types (strings where integers are expected, or vice versa).
tputs
  returns an error if the string parameter is null. It does not detect I/O errors: X/Open states that tputs ignores the return value of the output function putc.

## 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,

# HISTORY

SVr2 introduced the terminfo feature. Its programming manual mentioned these low-level functions:

Function | Description
fixterm | restore tty to “in curses” state
gettmode | establish current tty modes
mvcur | low level cursor motion
putp | utility function that uses tputs to send characters via putchar.
resetterm | set tty modes to “out of curses” state
resetty | reset tty flags to stored value
saveterm | save current modes as “in curses” state
savetty | store current tty flags
setterm | establish terminal with given type
setupterm | establish terminal with given type
tparm | instantiate a string expression with parameters
tputs | apply padding information to a string
vidattr | like vidputs, but outputs through putchar
vidputs | output a string to put terminal in a specified video attribute mode

The programming manual also mentioned functions provided for termcap compatibility (commenting that they “may go away at a later date”):

Function | Description
tgetent | look up termcap entry for given name
tgetflag | get boolean entry for given id
tgetnum | get numeric entry for given id
tgetstr | get string entry for given id
tgoto | apply parameters to given capability
tputs | apply padding to capability, calling a function to put characters

Early terminfo programs obtained capability values from the TERMINAL structure initialized by setupterm.

SVr3 extended terminfo by adding functions to retrieve capability values (like the termcap interface), and reusing tgoto and tputs:

Function | Description
tigetflag | get boolean entry for given id
tigetnum | get numeric entry for given id
tigetstr | get string entry for given id

SVr3 also replaced several of the SVr2 terminfo functions which had no counterpart in the termcap interface, documenting them as obsolete:

Function | Replaced by
crmode | cbreak
fixterm | reset_prog_mode
gettmode | N/A
nocrmode | nocbreak
resetterm | reset_shell_mode
saveterm | def_prog_mode
setterm | setupterm

SVr3 kept the mvcur, vidattr and vidputs functions, along with putp, tparm and tputs. The latter were needed to support padding, and handling functions such as vidattr (which used more than the two parameters supported by tgoto).

SVr3 introduced the functions for switching between terminal descriptions, e.g., set_curterm. Some of that was incremental improvements to the SVr2 library:

- The TERMINAL type definition was introduced in SVr3.01, for the term structure provided in SVr2.
- The various global variables such as boolnames were mentioned in the programming manual at this point, though the variables were provided in SVr2.

SVr4 added the vid_attr and vid_puts functions.

There are other low-level functions declared in the curses header files on Unix systems, but none were documented. The functions marked “obsolete” remained in use by the Unix vi(1) editor.

# PORTABILITY

## Extensions

The functions marked as extensions were designed for ncurses(3), and are not found in SVr4 curses, 4.4BSD curses, or any other previous version of curses.

## 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.
  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:

•
  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).

•
  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 (e.g., 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 tput(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, e.g., for the MinGW port,

•
  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 gn (generic_type) terminfo capability, while the latter does not. A generic terminal is unsuitable for full-screen applications.

•
  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.

# SEE ALSO

curses(3), curs_initscr(3), curs_kernel(3), curs_memleaks(3), termcap(3), curs_variables(3), term_variables(3), putc(3), terminfo(5)

2023-08-19 | ncurses 6.4