[The following is a markup of an article by the author posted to comp.lang.c and comp.lang.c.moderated in December 1996 -- Jens Schweikhardt]

hello, world\n

this is a message to all those concerned about C Standard compliance on both sides of the fence, that is, users and vendors.

Okay, enough hype. If you're still with me here you might find it valuable and enlightening if you read the next few dozen lines and take appropriate actions. And no, this is not about me or you making money fast, I swear.


Jens -- The man with a mission :-)

Jens Schweikhardt <schweikh@schweikhardt.net>


Download the iso-mac.c source below (de-HTMLized, 16k ASCII).

 * iso-mac.c - check system headers for ISO 9899:1990 compliance
 * This is a simple minded program that tries to find illegal macro
 * definitions in system header files. Illegal macro definitions are
 * those not from the implementation name space (i.e. not starting with
 * an underscore) or not matching any identifier mandated by The
 * Standard. Some common macro names are considered okay, e.g. all those
 * beginning with E (which may be defined in <errno.h>) or ending in
 * _MAX. See the arrays prefix[] and suffix[] below for details.
 * In a compliant implementation no other macros can be defined, because
 * you could write strictly conforming programs that may fail to compile
 * due to syntax errors: suppose <stdio.h> defines PIPE_BUF, then the
 * conforming
 * #include <assert.h>
 * #include <stdio.h>      <- or where the bogus macro is defined
 * #include <string.h>
 * #define STR(x) #x
 * #define XSTR(x) STR(x)
 * int main (void)
 * {
 *    int PIPE_BUF = 0;
 *    assert (strcmp ("PIPE_BUF", XSTR (PIPE_BUF)) == 0);
 *    return 0;
 * }
 * is expected to compile and meet the assertion. If it does not, your
 * compiler compiles some other language than Standard C.
 *   This program calls gcc to get the list of defined macros. If you
 *   don't have gcc you're probably out of luck unless your compiler or
 *   preprocessor has something similar to gcc's -dM option. Tune
 *   PRINT_MACROS in this case. This program assumes headers are found
 *   under /usr/include and that there is a writable /tmp directory.
 *   Tune SYSTEM_INCLUDE and TMPFILE if your system differs.
 *   cc iso-mac.c -o iso-mac      # any ISO C compiler will do
 *   ./iso-mac                    # simply run isomac without args
 *   Each header file name is printed, followed by illegal macro names
 *   and their definition. For the above example, you would see
 *   ...
 *   /usr/include/stdio.h
 *   #define PIPE_BUF 5120
 *   ...
 *   If your implementation does not yet incorporate Amendment 1 you
 *   will see messages about iso646.h, wctype.h and wchar.h not being
 *   found.
 *   Look at the header file and verify that the macro is really visible
 *   when your compiler is in *strict* ANSI/ISO C mode. This is
 *   important! Gcc needs -ansi -pedantic, some other compilers use -Xa.
 *   Usually this will define the macro __STDC__. The vendor extensions
 *   should be wrapped in an #ifndef __STDC__ or something similar. Then
 *   compile and run the above program. If a syntax error occurs or the
 *   assertion fails complain to whoever is responsible for the header
 *   files (note that this may *not* be your compiler vendor, but rather
 *   your system vendor) and ask whether they claim ISO C conformance.
 *   Most will (should) blush :-) I explicitly encourage you to send
 *   them this source in your bug report.
 *   If Amendment 1 headers are missing, bug your vendor for an upgrade.
 *   You can do everything you want with this source except pretend that
 *   you wrote it. Credit where credit is due. Fair enough, isn't it?
 *   Jens Schweikhardt <schweikh@schweikhardt.net>
 *   Corrections and suggestions welcome.
 *   You get what you pay for. I won't pay for anything you get or will
 *   not get by using this program. Again, fair enough, isn't it?

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define TMPFILE             "/tmp/macros"
#define SYSTEM_INCLUDE      "/usr/include"
#define HEADER_MAX          (sizeof SYSTEM_INCLUDE "/123456.h")
#define PRINT_MACROS        "gcc -E -dM -ansi -pedantic -I" SYSTEM_INCLUDE
#define COMMAND_MAX         256

/* ISO C header names including Amendment 1 (without ".h" suffix) */
static char *header[] = {
    "assert", "ctype", "errno", "float", "iso646", "limits", "locale",
    "math", "setjmp", "signal", "stdarg", "stddef", "stdio", "stdlib",
    "string", "time", "wchar", "wctype"

/* Macros with these prefixes are considered okay */
static char *prefix[] = {
    "_", "E", "is", "str", "mem", "SIG", "FLT_", "DBL_", "LDBL_",
    "LC_", "wmem", "wcs"

 * Macros with these suffixes are considered okay.
 * Will not work for parameterized macros with arguments.
static char *suffix[] = {
    "_MAX", "_MIN"

/* These macros are considered okay. In fact, these are just more prefixes. */
static char *macros[] = {
    "LDBL_MIN_EXP", "LONG_MAX", "LONG_MIN", "L_tmpnam", "MB_CUR_MAX",
    "WEOF", "_IOFBF", "_IOLBF", "_IONBF", "abort", "abs", "acos",
    "acosf", "acosl", "and", "and_eq", "asctime", "asin", "asinf",
    "asinl", "assert", "atan", "atan2", "atan2f", "atan2l", "atanf",
    "atanl", "atexit", "atof", "atoi", "atol", "bitand", "bitor",
    "bsearch", "btowc", "calloc", "ceil", "ceilf", "ceill", "clearerr",
    "clock", "clock_t", "compl", "cos", "cosf", "cosh", "coshf",
    "coshl", "cosl", "ctime", "difftime", "div", "div_t", "errno",
    "exit", "exp", "expf", "expl", "fabs", "fabsf", "fabsl", "fclose",
    "feof", "ferror", "fflush", "fgetc", "fgetpos", "fgets", "fgetwc",
    "fgetws", "floor", "floorf", "floorl", "fmod", "fmodf", "fmodl",
    "fopen", "fprintf", "fputc", "fputs", "fputwc", "fputws", "fread",
    "free", "freopen", "frexp", "frexpf", "frexpl", "fscanf", "fseek",
    "fsetpos", "ftell", "fwide", "fwprintf", "fwrite", "fwscanf",
    "getc", "getchar", "getenv", "gets", "getwc", "getwchar", "gmtime",
    "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower",
    "isprint", "ispunct", "isspace", "isupper", "iswalnum", "iswalpha",
    "iswcntrl", "iswctype", "iswdigit", "iswgraph", "iswlower",
    "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
    "isxdigit", "labs", "ldexp", "ldexpf", "ldexpl", "ldiv", "ldiv_t",
    "localeconv", "localtime", "log", "log10", "log10f", "log10l",
    "logf", "logl", "longjmp", "malloc", "mblen", "mbrlen", "mbrtowc",
    "mbsinit", "mbsrtowcs", "mbstate_t", "mbstowcs", "mbtowc", "memchr",
    "memcmp", "memcpy", "memmove", "memset", "mktime", "modf", "modff",
    "modfl", "not", "not_eq", "offsetof", "or", "or_eq", "perror",
    "pow", "powf", "powl", "printf", "ptrdiff_t", "putc", "putchar",
    "puts", "putwc", "putwchar", "qsort", "raise", "rand", "realloc",
    "remove", "rename", "rewind", "scanf", "setbuf", "setjmp",
    "setlocale", "setvbuf", "sig_atomic_t", "signal", "sin", "sinf",
    "sinh", "sinhf", "sinhl", "sinl", "size_t", "sprintf", "sqrt",
    "sqrtf", "sqrtl", "srand", "sscanf", "stderr", "stdin", "stdout",
    "strcat", "strchr", "strcmp", "strcoll", "strcpy", "strcspn",
    "strerror", "strftime", "strlen", "strncat", "strncmp", "strncpy",
    "strpbrk", "strrchr", "strspn", "strstr", "strtod", "strtok",
    "strtol", "strtoul", "strxfrm", "swprintf", "swscanf", "system",
    "tan", "tanf", "tanh", "tanhf", "tanhl", "tanl", "time", "time_t",
    "tmpfile", "tmpnam", "tolower", "toupper", "towctrans", "towlower",
    "towupper", "ungetc", "ungetwc", "va_arg", "va_end", "va_start",
    "vfprintf", "vfwprintf", "vprintf", "vsprintf", "vswprintf",
    "vwprintf", "wchar_t", "wcrtomb", "wcscat", "wcschr", "wcscmp",
    "wcscoll", "wcscpy", "wcscspn", "wcsftime", "wcslen", "wcsncat",
    "wcsncmp", "wcsncpy", "wcspbrk", "wcsrchr", "wcsrtombs", "wcsspn",
    "wcsstr", "wcstod", "wcstok", "wcstol", "wcstombs", "wcstoul",
    "wcsxfrm", "wctob", "wctomb", "wctrans", "wctrans_t", "wctype",
    "wctype_t", "wint_t", "wmemchr", "wmemcmp", "wmemcpy", "wmemmove",
    "wmemset", "wprintf", "wscanf", "xor", "xor_eq"

#define NUMBER_OF_HEADERS              (sizeof header/sizeof *header)
#define NUMBER_OF_PREFIXES             (sizeof prefix/sizeof *prefix)
#define NUMBER_OF_SUFFIXES             (sizeof suffix/sizeof *suffix)
#define NUMBER_OF_MACROS               (sizeof macros/sizeof *macros)

static void check_header (char *);

main (void)
    int h;

    if (system (NULL) == 0) {
        fprintf (stderr, "sorry, no command processor\n");
        return EXIT_FAILURE;
    for (h = 0; h < NUMBER_OF_HEADERS; ++h) {
        char file_name[HEADER_MAX];
        sprintf (file_name, SYSTEM_INCLUDE "/%s.h", header[h]);
        check_header (file_name);
    return EXIT_SUCCESS;

    static void
check_header (char *file_name)
    char line[BUFSIZ], command[COMMAND_MAX];
    FILE *input;

    puts (file_name);
    sprintf (command, "%s %s > %s", PRINT_MACROS, file_name, TMPFILE);
    if (system (command))
        fprintf (stderr, "system() returned nonzero\n");
    input = fopen (TMPFILE, "r");

    if (input == NULL) {
        fprintf (stderr, "could not read %s: ", TMPFILE);
        perror (NULL);

    while (fgets (line, sizeof line, input) != NULL) {
        int i, okay = 0;
        char *space2 = strchr (line + 8, ' ');
        for (i = 0; i < NUMBER_OF_PREFIXES; ++i) {
            if (!strncmp (line+8, prefix[i], strlen (prefix[i]))) {
        if (okay) continue;
        for (i = 0; i < NUMBER_OF_MACROS; ++i) {
            if (!strncmp (line+8, macros[i], strlen (macros[i]))) {
        if (okay) continue;
        for (i = 0; i < NUMBER_OF_SUFFIXES; ++i) {
            size_t len = strlen (suffix[i]);
            if (!strncmp (space2 - len, suffix[i], len)) {
        if (!okay) fputs (line, stdout);
    fclose (input);
    remove (TMPFILE);

/* EOF */

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