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Full Discussion: C- static initialization of structures
Top Forums Programming C- static initialization of structures Post 302744943 by jim mcnamara on Sunday 16th of December 2012 01:05:33 AM
Old 12-16-2012
No.

Code:
Since tags_sn = "heck"; works, so should tags_sn = (void *)0;

tags_sn is properly initialized with '\0', or {0x0}; not NULL
Code:
(void *)0.

Why? the standard says that tags_sn is an array. Valid ways to initialize an array of char all NUL is to use the { } construct or a zero. In either case the first element of the array is set to what is inside { } or to zero, all successive bytes are set to zero.


Code:
   struct my_struct_type {
        char tags_sn[5];
        char group_c;
        char is_err_c;
    };
    struct my_struct_type stuff[] = {
        {"abcd", 'A', 'E'},
        {"efgh", 'B', 'E'},
        {"ijkl", 'C', 'E'},
        { {0x0}, '\0', '\0'}
    };
    
int main()
{
	 int i=0;
	 for(i=0; *stuff[i].tags_sn; i++)  
	    printf("%d\n", i);
	 return 0;   
}

Note the red changes, this code ran identically to the first corrected version.
Code:
$ ./a.out
0
1
2

An array declaration is not a pointer, nor is an array a pointer. A reference to an array is a pointer. That is why the *stuff thing works,
but assigning NULL to an array does not work correctly. In K & R a zero is the equivalent of a NULL in a pointer context. The NULL as well as void -- came later. This (char *)0 construct made a NULL in K & R, and its use carried forward. There was no void to start with.
Last edited by jim mcnamara; 12-16-2012 at 02:14 AM..
 

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LEARN ABOUT FREEBSD

config.guess

CONFIG.GUESS(1) 						   User Commands						   CONFIG.GUESS(1)

NAME

       config.guess - guess the build system triplet

SYNOPSIS

       config.guess [OPTION]

DESCRIPTION

       The GNU build system distinguishes three types of machines, the `build' machine on which the compilers are run, the `host' machine on which
       the package being built will run, and, exclusively when you build a compiler, assembler etc., the `target' machine, for which the  compiler
       being built will produce code.

       This script will guess the type of the `build' machine.

       Output the configuration name of the system `config.guess' is run on.

   Operation modes:
       -h, --help
	      print this help, then exit

       -t, --time-stamp
	      print date of last modification, then exit

       -v, --version
	      print version number, then exit

ENVIRONMENT VARIABLES

       config.guess  might  need  to  compile  and  run  C  code,  hence it needs a compiler for the `build' machine: use the environment variable
       `CC_FOR_BUILD' to specify the compiler for the build machine.  If `CC_FOR_BUILD' is not specified, `CC' will be used.  Be sure  to  specify
       `CC_FOR_BUILD' is `CC' is a cross-compiler to the `host' machine.

	 CC_FOR_BUILD	 a native C compiler, defaults to `cc'
	 CC		 a native C compiler, the previous variable is preferred

REPORTING BUGS

       Report bugs and patches to <config-patches@gnu.org>.

       Originally written by Per Bothner.
       Copyright 1992-2016 Free Software Foundation, Inc.

       This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
       LAR PURPOSE.

SEE ALSO

       autoconf(1), automake(1), autoreconf(1), autoupdate(1), autoheader(1), autoscan(1), config.guess(1), config.sub(1), ifnames(1), libtool(1).

GNU Autoconf 2.69						    August 2017 						   CONFIG.GUESS(1)
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