c - Windows 7 x64 上的 tmpfile()

Question

在 Windows 7 x64 上运行以下代码

#include <stdio.h>
#include <errno.h>

int main() {
    int i;
    FILE *tmp;
    for (i = 0; i < 10000; i++) {
        errno = 0;
        if(!(tmp = tmpfile())) printf("Fail %d, err %d\n", i, errno);
        fclose(tmp);
    }
    return 0;
}

在第 637 次和第 1004 次调用时给出错误号 13(权限被拒绝)，它在 XP 上工作正常(还没有尝试过 7 x86)。我是否遗漏了什么或者这是一个错误？

Answer 1

我在 Windows 8 上遇到了类似的问题 - tmpfile() 导致了 win32 ERROR_ACCESS_DENIED 错误代码 - 是的，如果您以管理员权限运行应用程序 - 那么它工作正常。

我想这里提到了问题: https://lists.gnu.org/archive/html/bug-gnulib/2007-02/msg00162.html

Under Windows, the tmpfile function is defined to always create its temporary file in the root directory. Most users don't have permission to do that, so it will often fail.

我怀疑这是一个不完整的 Windows 端口问题 - 所以这应该是向 Microsoft 报告的错误。 (如果没有用，为什么要编写 tmpfile 函数？)

但是谁有时间和微软的风车打架呢？! :-)

我使用 GetTempPathW/GetModuleFileNameW/_wfopen 编写了类似的实现。我遇到此问题的代码来自 libjpeg - 我在此处附加了完整的源代码，但您可以从 jpeg_open_backing_store 中获取代码。

jmemwin.cpp:

//
//  Windows port for jpeg lib functions.
//
#define JPEG_INTERNALS
#include <Windows.h>        // GetTempFileName
#undef FAR                  // Will be redefined - disable warning
#include "jinclude.h"
#include "jpeglib.h"

extern "C" {
#include "jmemsys.h"        // jpeg_ api interface.

//
// Memory allocation and freeing are controlled by the regular library routines malloc() and free().
//

GLOBAL(void *) jpeg_get_small (j_common_ptr cinfo, size_t sizeofobject)
{
    return (void *) malloc(sizeofobject);
}

GLOBAL(void) jpeg_free_small (j_common_ptr cinfo, void * object, size_t sizeofobject)
{
    free(object);
}

/*
 * "Large" objects are treated the same as "small" ones.
 * NB: although we include FAR keywords in the routine declarations,
 * this file won't actually work in 80x86 small/medium model; at least,
 * you probably won't be able to process useful-size images in only 64KB.
 */

GLOBAL(void FAR *) jpeg_get_large (j_common_ptr cinfo, size_t sizeofobject)
{
    return (void FAR *) malloc(sizeofobject);
}

GLOBAL(void) jpeg_free_large (j_common_ptr cinfo, void FAR * object, size_t sizeofobject)
{
    free(object);
}

//
//  Used only by command line applications, not by static library compilation
//
#ifndef DEFAULT_MAX_MEM     /* so can override from makefile */
#define DEFAULT_MAX_MEM     1000000L /* default: one megabyte */
#endif

GLOBAL(long) jpeg_mem_available (j_common_ptr cinfo, long min_bytes_needed, long max_bytes_needed, long already_allocated)
{
    // jmemansi.c's jpeg_mem_available implementation was insufficient for some of .jpg loads.
    MEMORYSTATUSEX status = { 0 };
    status.dwLength = sizeof(status);
    GlobalMemoryStatusEx(&status);

    if( status.ullAvailPhys > LONG_MAX )
        // Normally goes here since new PC's have more than 4 Gb of ram.
        return LONG_MAX;

    return (long) status.ullAvailPhys;
}


/*
    Backing store (temporary file) management.
    Backing store objects are only used when the value returned by
    jpeg_mem_available is less than the total space needed.  You can dispense
    with these routines if you have plenty of virtual memory; see jmemnobs.c.
*/

METHODDEF(void) read_backing_store (j_common_ptr cinfo, backing_store_ptr info, void FAR * buffer_address, long file_offset, long byte_count)
{
    if (fseek(info->temp_file, file_offset, SEEK_SET))
        ERREXIT(cinfo, JERR_TFILE_SEEK);

    size_t readed = fread( buffer_address, 1, byte_count, info->temp_file);

    if (readed != (size_t) byte_count)
        ERREXIT(cinfo, JERR_TFILE_READ);
}


METHODDEF(void)
write_backing_store (j_common_ptr cinfo, backing_store_ptr info, void FAR * buffer_address, long file_offset, long byte_count)
{
    if (fseek(info->temp_file, file_offset, SEEK_SET))
        ERREXIT(cinfo, JERR_TFILE_SEEK);

    if (JFWRITE(info->temp_file, buffer_address, byte_count) != (size_t) byte_count)
        ERREXIT(cinfo, JERR_TFILE_WRITE);

    // E.g. if you need to debug writes.
    //if( fflush(info->temp_file) != 0 )
    //    ERREXIT(cinfo, JERR_TFILE_WRITE);
}


METHODDEF(void)
close_backing_store (j_common_ptr cinfo, backing_store_ptr info)
{
    fclose(info->temp_file);
    // File is deleted using 'D' flag on open.
}

static HMODULE DllHandle()
{
    MEMORY_BASIC_INFORMATION info;
    VirtualQuery(DllHandle, &info, sizeof(MEMORY_BASIC_INFORMATION));
    return (HMODULE)info.AllocationBase;
}

GLOBAL(void) jpeg_open_backing_store(j_common_ptr cinfo, backing_store_ptr info, long total_bytes_needed)
{
    // Generate unique filename.
    wchar_t path[ MAX_PATH ] = { 0 };
    wchar_t dllPath[ MAX_PATH ] = { 0 };
    GetTempPathW( MAX_PATH, path );

    // Based on .exe or .dll filename
    GetModuleFileNameW( DllHandle(), dllPath, MAX_PATH );

    wchar_t* p = wcsrchr( dllPath, L'\\');
    wchar_t* ext = wcsrchr( p + 1, L'.');

    if( ext ) *ext = 0;
    wchar_t* outFile = path + wcslen(path);

    static int iTempFileId = 1;
    // Based on process id (so processes would not fight with each other)
    // Based on some process global id.
    wsprintfW(outFile, L"%s_%d_%d.tmp",p + 1, GetCurrentProcessId(), iTempFileId++ );

    // 'D' - temporary file.
    if ((info->temp_file = _wfopen(path, L"w+bD") ) == NULL)
        ERREXITS(cinfo, JERR_TFILE_CREATE, "");

    info->read_backing_store = read_backing_store;
    info->write_backing_store = write_backing_store;
    info->close_backing_store = close_backing_store;
} //jpeg_open_backing_store


/*
 * These routines take care of any system-dependent initialization and
 * cleanup required.
 */

GLOBAL(long)
jpeg_mem_init (j_common_ptr cinfo)
{
     return DEFAULT_MAX_MEM;    /* default for max_memory_to_use */
}

GLOBAL(void)
jpeg_mem_term (j_common_ptr cinfo)
{
  /* no work */
}

}

我故意忽略了一些函数的错误——你见过 GetTempPathW 或 GetModuleFileNameW 失败吗？