intro(3)                                                 intro(3)



     NAME
          intro - introduction to subroutines and libraries

     SYNOPSIS
          #include <stdio.h>

          #include <math.h>

     DESCRIPTION
          This section describes functions found in various libraries,
          other than those functions that directly invoke system
          primitives, which are described in Section 2 of this volume.
          Certain major collections are identified by a letter after
          the section number:

          (3C)  These functions, together with those of Section 2 and
                those marked (3S), constitute the Standard C Library,
                libc, which is automatically loaded by the C compiler,
                cc(1).  The link editor ld(1) searches this library
                under the -lc option.  Some functions require
                declarations that can be included in the program being
                compiled by adding the line

                #include <header filename>

                The appropriate #include file is indicated in the
                SYNOPSIS part of a function description.
          (3F)  These functions constitute the FORTRAN intrinsic
                function library, libF77.  These functions are
                automatically available to the FORTRAN programmer and
                require no special invocation of the compiler.
          (3M)  These functions constitute the Math Library, libm.
                They are automatically loaded as needed by the FORTRAN
                compiler f77(1).  They are not automatically loaded by
                the C compiler, cc(1); however, the link editor
                searches this library under the -lm option.
                Declarations for these functions may be obtained from
                the #include file <math.h>.
          (3S)  These functions constitute the ``standard I/O
                package'';  an introduction to this package is
                provided in stdio(3S).  The functions are in the
                library libc, already mentioned.  Declarations should
                be obtained from the #include file <stdio.h>.
          (3X)  Various specialized libraries.  The files in which
                these libraries are found are given on the appropriate
                pages.

                For descriptions and examples of #include files, refer
                to the sections on libraries in Oreo Programming
                Languages and Tools, Volume 1.  Guide.

     DEFINITIONS



     Page 1                                        (last mod. 1/14/87)

     intro(3)                                                 intro(3)



          A character is any bit pattern able to fit into a byte on
          the machine.  The null character is a character with value
          0, represented in the C language as '\0'.  A character array
          is a sequence of characters.  A null-terminated character
          array is a sequence of characters, the last of which is the
          null character.  A string is a designation for a null-
          terminated character array.  The null string  is a character
          array containing only the null character.  A NULL pointer is
          the value that is obtained by casting 0 into a pointer.  The
          C language guarantees that this value will not match that of
          any legitimate pointer, so many functions that return
          pointers return it to indicate an error.  NULL is defined as
          0 in <stdio.h>; the user can include his own definition if
          he is not using <stdio.h>.

          Many groups of FORTRAN intrinsic functions have generic
          function names that do not require explicit or implicit type
          declaration.  The type of the function is determined by the
          type of its argument(s).  For example, the generic function
          max returns an integer value if given integer arguments
          (max0), a real value if given real arguments (amax1), or a
          double-precision value if given double-precision arguments
          (dmax1).

     FILES
          /lib/libc.a
          /usr/lib/libF77.a
          /lib/libm.a

     SEE ALSO
          ar(1), cc(1), f77(1), ld(1), lint(1), nm(1), intro(2),
          stdio(3S), math(5).  Oreo Programming Languages and Tools,
          Volume 1.

     DIAGNOSTICS
          Functions in the C and Math Libraries (3C and 3M) may return
          the conventional values 0 or +HUGE (the largest-magnitude
          single-precision floating-point numbers; HUGE is defined in
          the <math.h> header file) when the function is undefined for
          the given arguments or when the value is not representable.
          In these cases, the external variable errno (see intro(2))
          is set to the value EDOM or ERANGE.  Because many of the
          FORTRAN intrinsic functions use the routines found in the
          Math Library, the same conventions apply.

     WARNING
          Many of the functions in the libraries call and/or refer to
          other functions and external variables described in this
          section and in section 2 (System Calls).  If a program
          inadvertantly defines a function or external variable with
          the same name, the presumed library version of the function
          or external variable may not be loaded.  The lint(1) program



     Page 2                                        (last mod. 1/14/87)

     intro(3)                                                 intro(3)



          checker reports name conflicts of this kind as ``multiple
          declarations'' of the names in question.  Definitions for
          sections 2, 3C, and 3S are checked automatically.  Other
          definitions can be included by using the -l option (for
          example, -lm includes definitions for the Math Library,
          section 3M).  Use of lint is highly recommended.

















































     Page 3                                        (last mod. 1/14/87)