c - 不明确的错误 "...undeclared (first use in this function)"

Question

无论出于何种原因，MinGW 的 gcc 似乎无法找到该变量的“#define” block 。完整的错误是

.../mapped.c:396:28: error: '_zzip_strcasecmp' undeclared (first use in this function)

mapped.c 的内容:

/*
 * NOTE: this is part of libzzipmmapped (i.e. it is not libzzip).
 *                                            ==================
 *
 * These routines are fully independent from the traditional zzip
 * implementation. They assume a readonly mmapped sharedmem block
 * representing a complete zip file. The functions show how to 
 * parse the structure, find files and return a decoded bytestream.
 *
 * These routines are a bit simple and really here for documenting
 * the way to access a zip file. The complexity of zip access comes
 * from staggered reading of bytes and reposition of a filepointer in
 * a big archive with lots of files and long compressed datastreams.
 * Plus varaints of drop-in stdio replacements, obfuscation routines,
 * auto fileextensions, drop-in dirent replacements, and so on...
 *
 * Author: 
 *      Guido Draheim <guidod@gmx.de>
 *
 * Copyright (c) 2003,2004,2006 Guido Draheim
 *          All rights reserved,
 *          use under the restrictions of the 
 *          Lesser GNU General Public License
 *          or alternatively the restrictions 
 *          of the Mozilla Public License 1.1
 */

#define _ZZIP_DISK_FILE_STRUCT 1

#ifdef __linux__
#define _GNU_SOURCE _glibc_developers_are_idiots_to_call_strndup_gnu_specific_
#endif

#include <zzip/mmapped.h>
#include <zzip/format.h>
#include <zzip/fetch.h>
#include <zzip/__mmap.h>
#include <zzip/__fnmatch.h>

#include <stdlib.h>
#include <sys/stat.h>

#if   defined ZZIP_HAVE_UNISTD_H
#include <unistd.h>
#elif defined ZZIP_HAVE_IO_H
#include <io.h>
#endif

#if   defined ZZIP_HAVE_STRING_H
#include <string.h>
#elif defined ZZIP_HAVE_STRINGS_H
#include <strings.h>
#endif


#if __STDC_VERSION__+0 > 199900L
#define ___
#define ____
#else
#define ___ {
#define ____ }
#endif

/** => zzip_disk_mmap
 * This function does primary initialization of a disk-buffer struct.
 */
int
zzip_disk_init(ZZIP_DISK* disk, void* buffer, zzip_size_t buflen)
{
    disk->buffer = (zzip_byte_t*) buffer;
    disk->endbuf = (zzip_byte_t*) buffer + buflen;
    disk->reserved = 0;
    disk->flags = 0;
    disk->mapped = 0;
    /* do not touch disk->user */
    /* do not touch disk->code */
    return 0;
}

/** => zzip_disk_mmap
 * This function allocates a new disk-buffer with => malloc(3)
 */
zzip__new__ ZZIP_DISK*
zzip_disk_new(void)
{
    ZZIP_DISK* disk = malloc(sizeof(disk));
    if (! disk) return disk;
    zzip_disk_init (disk, 0, 0);
    return disk;
}

/** turn a filehandle into a mmapped zip disk archive handle
 *
 * This function uses the given file-descriptor to detect the length of the 
 * file and calls the system => mmap(2) to put it in main memory. If it is
 * successful then a newly allocated ZZIP_DISK* is returned with 
 * disk->buffer pointing to the mapview of the zipdisk content.
 */
zzip__new__ ZZIP_DISK*
zzip_disk_mmap(int fd)
{
    struct stat st;
    if (fstat (fd, &st) || ! st.st_size) return 0;
    ___ ZZIP_DISK* disk = zzip_disk_new (); if (! disk) return 0;
    disk->buffer = _zzip_mmap (& disk->mapped, fd, 0, st.st_size);
    if (disk->buffer == MAP_FAILED) { free (disk); return 0; }
    disk->endbuf = disk->buffer + st.st_size;
    return disk; ____;
}

/** => zzip_disk_mmap
 * This function is the inverse of => zzip_disk_mmap and using the system
 * munmap(2) on the buffer area and => free(3) on the ZZIP_DISK structure.
 */
int
zzip_disk_munmap(ZZIP_DISK* disk)
{
    if (! disk) return 0;
    _zzip_munmap (disk->mapped, disk->buffer, disk->endbuf-disk->buffer);
    free (disk);
    return 0;
}

/** => zzip_disk_mmap
 *
 * This function opens the given archive by name and turn the filehandle 
 * to  => zzip_disk_mmap for bringing it to main memory. If it can not
 * be => mmap(2)'ed then we slurp the whole file into a newly => malloc(2)'ed
 * memory block. Only if that fails too then we return null. Since handling
 * of disk->buffer is ambigous it should not be snatched away please.
 */
ZZIP_DISK* zzip__new__
zzip_disk_open(char* filename)
{
#  ifndef O_BINARY
#  define O_BINARY 0
#  endif
    struct stat st;
    if (stat (filename, &st) || ! st.st_size) return 0;
    ___ int fd = open (filename, O_RDONLY|O_BINARY);
    if (fd <= 0) return 0;
    ___ ZZIP_DISK* disk = zzip_disk_mmap (fd);
    if (disk) return disk;
    ___ zzip_byte_t* buffer = malloc (st.st_size);
    if (! buffer) return 0;
    if ((st.st_size == read (fd, buffer, st.st_size)) &&
    (disk = zzip_disk_new ())) 
    {
    disk->buffer = buffer;
    disk->endbuf = buffer+st.st_size;
    disk->mapped = -1;
    }else free (buffer);
    return disk; ____;____;____;
}

/** => zzip_disk_mmap
 * 
 * This function will release all data needed to access a (mmapped)
 * zip archive, including any malloc()ed blocks, sharedmem mappings
 * and it dumps the handle struct as well.
 */
int
zzip_disk_close(ZZIP_DISK* disk)
{
    if (! disk) return 0;
    if (disk->mapped != -1) return zzip_disk_munmap (disk);
    free (disk->buffer);
    free (disk);
    return 0;
}

/* ====================================================================== */
/*                      helper functions                                  */

#ifdef ZZIP_HAVE_STRNDUP
#define _zzip_strndup strndup
#else
/* if your system does not have strndup: */
zzip__new__ static char* _zzip_strndup(char* p, size_t maxlen)
{
    if (! p) return 0;
    ___ zzip_byte_t* r = malloc (maxlen+1);
    if (! r) return r;
    strncpy (r, p, maxlen);
    r[maxlen] = '\0';
    return r; ____;
}
#endif

#if defined ZZIP_HAVE_STRCASECMP || defined strcasecmp
#define _zzip_strcasecmp strcasecmp
#else
/* if your system does not have strcasecmp: */
static int _zzip_strcasecmp(char* __zzip_restrict a, char* _zzip_restrict b)
{
    if (! a) return (b) ? 1 : 0;
    if (! b) return -1;
    while (1) 
    {
    int v = tolower(*a) - tolower(*b);
    if (v) return v;
    if (! *a) return 1;
    if (! *b) return -1;
    a++; b++;
    }
}
#endif

/** helper functions for (mmapped) zip access api
 *
 * This function augments the other zzip_disk_entry_* helpers: here we move 
 * a disk_entry pointer (as returned by _find* functions) into a pointer to
 * the data block right after the file_header. Only disk->buffer would be
 * needed to perform the seek but we check the mmapped range end as well.
 */
zzip_byte_t*
zzip_disk_entry_to_data(ZZIP_DISK* disk, struct zzip_disk_entry* entry)
{
    struct zzip_file_header* file = 
    zzip_disk_entry_to_file_header(disk, entry);
    if (file) return zzip_file_header_to_data (file);
    return 0;
}

/** => zzip_disk_entry_to_data
 * This function does half the job of => zzip_disk_entry_to_data where it
 * can augment with => zzip_file_header_to_data helper from format/fetch.h
 */
struct zzip_file_header*
zzip_disk_entry_to_file_header(ZZIP_DISK* disk, struct zzip_disk_entry* entry)
{
    zzip_byte_t* file_header = /* (struct zzip_file_header*) */
    (disk->buffer + zzip_disk_entry_fileoffset (entry));
    if (disk->buffer > file_header || file_header >= disk->endbuf) 
    return 0;
    return (struct zzip_file_header*) file_header;
}

/** => zzip_disk_entry_to_data
 * This function is a big helper despite its little name: in a zip file the
 * encoded filenames are usually NOT zero-terminated but for common usage
 * with libc we need it that way. Secondly, the filename SHOULD be present
 * in the zip central directory but if not then we fallback to the filename
 * given in the file_header of each compressed data portion.
 */
zzip__new__ char*
zzip_disk_entry_strdup_name(ZZIP_DISK* disk, struct zzip_disk_entry* entry)
{
    if (! disk || ! entry) return 0;

    ___ char* name; zzip_size_t len;
    struct zzip_file_header* file;
    if ((len = zzip_disk_entry_namlen (entry)))
    name = zzip_disk_entry_to_filename (entry);
    else if ((file = zzip_disk_entry_to_file_header (disk, entry)) &&
         (len = zzip_file_header_namlen (file)))
    name = zzip_file_header_to_filename (file);
    else
    return 0;

    if ((zzip_byte_t*) name < disk->buffer || 
    (zzip_byte_t*) name+len > disk->endbuf)
    return 0;

    return  _zzip_strndup (name, len); ____;
}

/** => zzip_disk_entry_to_data
 * This function is similar creating a reference to a zero terminated
 * string but it can only exist in the zip central directory entry.
 */
zzip__new__ char*
zzip_disk_entry_strdup_comment(ZZIP_DISK* disk, struct zzip_disk_entry* entry)
{
    if (! disk || ! entry) return 0;

    ___ char* text; zzip_size_t len;
    if ((len = zzip_disk_entry_comment (entry)))
    text = zzip_disk_entry_to_comment (entry);
    else
    return 0;

    if ((zzip_byte_t*) text < disk->buffer || 
    (zzip_byte_t*) text+len > disk->endbuf)
    return 0;

    return  _zzip_strndup (text, len); ____;
}

/* ====================================================================== */

/** => zzip_disk_findfile
 *
 * This function is the first call of all the zip access functions here.
 * It contains the code to find the first entry of the zip central directory. 
 * Here we require the mmapped block to represent a real zip file where the
 * disk_trailer is _last_ in the file area, so that its position would be at 
 * a fixed offset from the end of the file area if not for the comment field 
 * allowed to be of variable length (which needs us to do a little search
 * for the disk_tailer). However, in this simple implementation we disregard 
 * any disk_trailer info telling about multidisk archives, so we just return
 * a pointer to the zip central directory.
 * 
 * For an actual means, we are going to search backwards from the end 
 * of the mmaped block looking for the PK-magic signature of a 
 * disk_trailer. If we see one then we check the rootseek value to
 * find the first disk_entry of the root central directory. If we find
 * the correct PK-magic signature of a disk_entry over there then we 
 * assume we are done and we are going to return a pointer to that label.
 *
 * The return value is a pointer to the first zzip_disk_entry being checked
 * to be within the bounds of the file area specified by the arguments. If
 * no disk_trailer was found then null is returned, and likewise we only 
 * accept a disk_trailer with a seekvalue that points to a disk_entry and 
 * both parts have valid PK-magic parts. Beyond some sanity check we try to
 * catch a common brokeness with zip archives that still allows us to find
 * the start of the zip central directory.
 */
struct zzip_disk_entry*
zzip_disk_findfirst(ZZIP_DISK* disk)
{
    if (disk->buffer > disk->endbuf-sizeof(struct zzip_disk_trailer))
    return 0;
    ___ zzip_byte_t* p = disk->endbuf-sizeof(struct zzip_disk_trailer);
    for (; p >= disk->buffer ; p--)
    {
    zzip_byte_t* root; /* (struct zzip_disk_entry*) */
    if (zzip_disk_trailer_check_magic(p)) {
        root =  disk->buffer + zzip_disk_trailer_get_rootseek (
        (struct zzip_disk_trailer*)p);
        if (root > p) 
        {   /* the first disk_entry is after the disk_trailer? can't be! */
        zzip_size_t rootsize = zzip_disk_trailer_get_rootsize (
            (struct zzip_disk_trailer*)p);
        if (disk->buffer+rootsize > p) continue;
        /* a common brokeness that can be fixed: we just assume the
         * central directory was written directly before the trailer:*/
        root = p - rootsize;
        }
    } else if (zzip_disk64_trailer_check_magic(p)) {
        if (sizeof(void*) < 8) return 0; /* EOVERFLOW */
        root =  disk->buffer + zzip_disk64_trailer_get_rootseek (
        (struct zzip_disk64_trailer*)p);
        if (root > p) continue; 
    } else continue;

    if (root < disk->buffer) continue;
    if (zzip_disk_entry_check_magic(root)) 
        return (struct zzip_disk_entry*) root;
    }____;
    return 0;
}

/** => zzip_disk_findfile
 *
 * This function takes an existing disk_entry in the central root directory
 * (e.g. from zzip_disk_findfirst) and returns the next entry within in
 * the given bounds of the mmapped file area.
 */
struct zzip_disk_entry*
zzip_disk_findnext(ZZIP_DISK* disk, struct zzip_disk_entry* entry)
{
    if ((zzip_byte_t*)entry < disk->buffer || 
    (zzip_byte_t*)entry > disk->endbuf-sizeof(entry) ||
    ! zzip_disk_entry_check_magic (entry) ||
    zzip_disk_entry_sizeto_end (entry) > 64*1024)
    return 0;
    entry = zzip_disk_entry_to_next_entry (entry);
    if ((zzip_byte_t*)entry > disk->endbuf-sizeof(entry) ||
    ! zzip_disk_entry_check_magic (entry) ||
    zzip_disk_entry_sizeto_end (entry) > 64*1024 ||
    zzip_disk_entry_skipto_end (entry) + sizeof(entry) > disk->endbuf)
    return 0;
    else
    return entry;
}

/** search for files in the (mmapped) zip central directory
 *
 * This function is given a filename as an additional argument, to find the 
 * disk_entry matching a given filename. The compare-function is usually 
 * strcmp or strcasecmp or perhaps strcoll, if null then strcmp is used. 
 * - use null as argument for "after"-entry when searching the first 
 * matching entry, otherwise the last returned value if you look for other
 * entries with a special "compare" function (if null then a doubled search
 * is rather useless with this variant of _findfile).
 */
struct zzip_disk_entry*
zzip_disk_findfile(ZZIP_DISK* disk, char* filename, 
            struct zzip_disk_entry* after, zzip_strcmp_fn_t compare)
{
    struct zzip_disk_entry* entry = (! after ? zzip_disk_findfirst (disk) 
                     : zzip_disk_findnext (disk, after));
    if (! compare) 
    compare = (zzip_strcmp_fn_t)( (disk->flags&1) ? 
                      (_zzip_strcasecmp) : (strcmp));
    for (; entry ; entry = zzip_disk_findnext (disk, entry))
    {
    /* filenames within zip files are often not null-terminated! */
    char* realname = zzip_disk_entry_strdup_name (disk, entry);
    if (realname && ! compare(filename, realname))
    {
        free (realname);
        return entry;
    }
    free (realname);
    }
    return 0;
}

/** => zzip_disk_findfile
 *
 * This function uses a compare-function with an additional argument
 * and it is called just like fnmatch(3) from POSIX.2 AD:1993), i.e.
 * the argument filespec first and the ziplocal filename second with
 * the integer-flags put in as third to the indirect call. If the
 * platform has fnmatch available then null-compare will use that one
 * and otherwise we fall back to mere strcmp, so if you need fnmatch
 * searching then please provide an implementation somewhere else.
 * - use null as argument for "after"-entry when searching the first 
 * matching entry, or the last disk_entry return-value to find the
 * next entry matching the given filespec.
 */
struct zzip_disk_entry*
zzip_disk_findmatch(ZZIP_DISK* disk, char* filespec, 
            struct zzip_disk_entry* after,
            zzip_fnmatch_fn_t compare, int flags)
{
    struct zzip_disk_entry* entry = (! after ? zzip_disk_findfirst (disk) 
                     : zzip_disk_findnext (disk, after));
    if (! compare) { 
    compare = (zzip_fnmatch_fn_t) _zzip_fnmatch; 
    if (disk->flags&1) disk->flags |= _zzip_fnmatch_CASEFOLD;
    }
    for (; entry ; entry = zzip_disk_findnext (disk, entry))
    {
    /* filenames within zip files are often not null-terminated! */
    char* realname = zzip_disk_entry_strdup_name(disk, entry);
    if (realname && ! compare(filespec, realname, flags))
    {
        free (realname);
        return entry;
    }
    free (realname);
    }
    return 0;
}

/* ====================================================================== */

/** => zzip_disk_fopen
 *
 * the ZZIP_DISK_FILE* is rather simple in just encapsulating the
 * arguments given to this function plus a zlib deflate buffer.
 * Note that the ZZIP_DISK pointer does already contain the full
 * mmapped file area of a zip disk, so open()ing a file part within
 * that area happens to be a lookup of its bounds and encoding. That
 * information is memorized on the ZZIP_DISK_FILE so that subsequent
 * _read() operations will be able to get the next data portion or
 * return an eof condition for that file part wrapped in the zip archive.
 */
zzip__new__ ZZIP_DISK_FILE*
zzip_disk_entry_fopen (ZZIP_DISK* disk, ZZIP_DISK_ENTRY* entry)
{
    /* keep this in sync with zzip_mem_entry_fopen */
    struct zzip_file_header* header = 
    zzip_disk_entry_to_file_header (disk, entry);
    if (! header) return 0;
    ___ ZZIP_DISK_FILE* file = malloc(sizeof(ZZIP_DISK_FILE));
    if (! file) return file;
    file->buffer = disk->buffer;
    file->endbuf = disk->endbuf;
    file->avail = zzip_file_header_usize (header);

    if (! file->avail || zzip_file_header_data_stored (header))
    { file->stored = zzip_file_header_to_data (header); return file; }

    file->stored = 0;
    file->zlib.opaque = 0;
    file->zlib.zalloc = Z_NULL;
    file->zlib.zfree = Z_NULL;
    file->zlib.avail_in = zzip_file_header_csize (header);
    file->zlib.next_in = zzip_file_header_to_data (header);

    if (! zzip_file_header_data_deflated(header) ||
        inflateInit2(&file->zlib, -MAX_WBITS) != Z_OK)
        { free (file); return 0; }

    return file;
    ____;
}

/** openening a file part wrapped within a (mmapped) zip archive
 *
 * This function opens a file found by name, so it does a search into
 * the zip central directory with => zzip_disk_findfile and whatever
 * is found first is given to => zzip_disk_entry_fopen
 */
zzip__new__ ZZIP_DISK_FILE*
zzip_disk_fopen (ZZIP_DISK* disk, char* filename)
{
    ZZIP_DISK_ENTRY* entry = zzip_disk_findfile (disk, filename, 0, 0);
    if (! entry) return 0; else return zzip_disk_entry_fopen (disk, entry);
}


/** => zzip_disk_fopen
 *
 * This function reads more bytes into the output buffer specified as
 * arguments. The return value is null on eof or error, the stdio-like
 * interface can not distinguish between these so you need to check
 * with => zzip_disk_feof for the difference.
 */
zzip_size_t
zzip_disk_fread (void* ptr, zzip_size_t sized, zzip_size_t nmemb,
         ZZIP_DISK_FILE* file)
{
    zzip_size_t size = sized*nmemb;
    if (size > file->avail) size = file->avail;
    if (file->stored)
    {
    memcpy (ptr, file->stored, size);
    file->stored += size;
    file->avail -= size;
    return size;
    }

    file->zlib.avail_out = sized*nmemb;
    file->zlib.next_out = ptr;
    ___ zzip_size_t total_old = file->zlib.total_out;
    ___ int err = inflate (& file->zlib, Z_NO_FLUSH);
    if (err == Z_STREAM_END)
    file->avail = 0;
    else if (err == Z_OK)
    file->avail -= file->zlib.total_out - total_old;
    else
    return 0;
    return file->zlib.total_out - total_old;
    ____;____;
}

/** => zzip_disk_fopen
 * This function releases any zlib decoder info needed for decompression
 * and dumps the ZZIP_DISK_FILE* then.
 */
int
zzip_disk_fclose (ZZIP_DISK_FILE* file)
{
    if (! file->stored)
    inflateEnd (& file->zlib);
    free (file);
    return 0;
}

/** => zzip_disk_fopen
 *
 * This function allows to distinguish an error from an eof condition. 
 * Actually, if we found an error but we did already reach eof then we
 * just keep on saying that it was an eof, so the app can just continue.
 */ 
int
zzip_disk_feof (ZZIP_DISK_FILE* file)
{
    return ! file || ! file->avail;
}

有人知道发生了什么事吗？抱歉，如果你们中的某些人可能看起来很明显，我是这方面的新手。

谢谢!

编辑: 由于我无法找出问题所在，我决定使用源代码附带的 visual studio 解决方案，并最终成功构建它。感谢所有试图帮助我解决这个问题的人。

Answer 1

错误的原因是在 C 语言中 () 中的名称不被视为宏。这实际上是专门为此目的而存在的语言功能:让您有机会在需要时“忽略”宏定义。

当您尝试使用 GCC 编译代码时，strcasecmp 似乎可用。 #if 的真正分支被编译器采用，这意味着 _zzip_strcasecmp 被定义为一个宏

#define _zzip_strcasecmp strcasecmp

只要你这样调用它就可以正常工作

_zzip_strcasecmp( /* whatever */ )

但是当您在此处将其称为 (_zzip_strcasecmp) 时，这将不起作用

compare = (zzip_strcmp_fn_t)( (disk->flags&1) ? 
                  (_zzip_strcasecmp) : (strcmp));

编译器将 (_zzip_strcasecmp) 视为在查找 _zzip_strcasecmp 时忽略宏的请求。编译器将查找 _zzip_strcasecmp 的非宏定义并失败并显示错误消息，因为这样的定义不存在。

当您在 Visual Siudio 中编译时，strcasecmp 不可用。 #if 的 false 分支被采用并且 _zzip_strcasecmp 在内部被定义为一个普通函数。所以，一切正常。

为宏版本修复它的一种方法是在有问题的错误语句中删除围绕函数名称的这些过多的 ()

compare = (zzip_strcmp_fn_t)( (disk->flags&1) ? 
                _zzip_strcasecmp : strcmp);

假设 strcasecmp 在那里确实可用，这应该在 GCC 中编译。

我不知道他们为什么把这些多余的 () 放在原始版本中。可能是“猖獗的括号”和被误导的“安全胜于遗憾”情绪的一个例子。实际上可能是故意这样做的，以防止在这种情况下使用宏(在这种情况下，坏人就是编写 #if 的人)。