SETBUF(3) BSD Programmer's Manual SETBUF(3) NNAAMMEE sseettbbuuff, sseettbbuuffffeerr, sseettlliinneebbuuff, sseettvvbbuuff - stream buffering operations SSYYNNOOPPSSIISS ##iinncclluuddee <<ssttddiioo..hh>> _v_o_i_d sseettbbuuff(_F_I_L_E _*_s_t_r_e_a_m, _c_h_a_r _*_b_u_f); _v_o_i_d sseettbbuuffffeerr(_F_I_L_E _*_s_t_r_e_a_m, _c_h_a_r _*_b_u_f, _s_i_z_e___t _s_i_z_e); _i_n_t sseettlliinneebbuuff(_F_I_L_E _*_s_t_r_e_a_m); _i_n_t sseettvvbbuuff(_F_I_L_E _*_s_t_r_e_a_m, _c_h_a_r _*_b_u_f, _i_n_t _m_o_d_e, _s_i_z_e___t _s_i_z_e); DDEESSCCRRIIPPTTIIOONN The three types of buffering available are unbuffered, block buffered, and line buffered. When an output stream is unbuffered, information ap- pears on the destination file or terminal as soon as written; when it is block buffered many characters are saved up and written as a block; when it is line buffered characters are saved up until a newline is output or input is read from any stream attached to a terminal device (typically stdin). The function fflush(3) may be used to force the block out early. (See fclose(3).) Normally all files are block buffered. When the first I/O operation oc- curs on a file, malloc(3) is called, and an optimally-sized buffer is ob- tained. If a stream refers to a terminal (as _s_t_d_o_u_t normally does) it is line buffered. The standard error stream _s_t_d_e_r_r is always unbuffered. The sseettvvbbuuff() function may be used to alter the buffering behavior of a stream. The _m_o_d_e parameter must be one of the following three macros: _IONBF unbuffered _IOLBF line buffered _IOFBF fully buffered The _s_i_z_e parameter may be given as zero to obtain deferred optimal-size buffer allocation as usual. If it is not zero, then except for un- buffered files, the _b_u_f argument should point to a buffer at least _s_i_z_e bytes long; this buffer will be used instead of the current buffer. (If the _s_i_z_e argument is not zero but _b_u_f is NULL, a buffer of the given size will be allocated immediately, and released on close. This is an exten- sion to ANSI C; portable code should use a size of 0 with any NULL buffer.) The sseettvvbbuuff() function may be used at any time, but may have peculiar side effects (such as discarding input or flushing output) if the stream is ``active''. Portable applications should call it only once on any given stream, and before any I/O is performed. The other three calls are, in effect, simply aliases for calls to sseettvvbbuuff(). Except for the lack of a return value, the sseettbbuuff() function is exactly equivalent to the call setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ); The sseettbbuuffffeerr() function is the same, except that the size of the buffer is up to the caller, rather than being determined by the default BUFSIZ. The sseettlliinneebbuuff() function is exactly equivalent to the call: setvbuf(stream, (char *)NULL, _IOLBF, 0); RREETTUURRNN VVAALLUUEESS The sseettvvbbuuff() function returns 0 on success, or EOF if the request cannot be honored (note that the stream is still functional in this case). The sseettlliinneebbuuff() function returns what the equivalent sseettvvbbuuff() would have returned. SSEEEE AALLSSOO fopen(3), fclose(3), fread(3), malloc(3), puts(3), printf(3) SSTTAANNDDAARRDDSS The sseettbbuuff() and sseettvvbbuuff() functions conform to ANSI C X3.159-1989 (``ANSI C ''). BBUUGGSS The sseettbbuuffffeerr() and sseettlliinneebbuuff() functions are not portable to versions of BSD before 4.2BSD. On 4.2BSD and 4.3BSD systems, sseettbbuuff() always uses a suboptimal buffer size and should be avoided. 4th Berkeley Distribution June 4, 1993 2