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旧的 MoreFilesX 中有一个很棒的功能，即 FSExchangeObjectsCompat，它“在两个文件之间交换数据”。它通常用作安全保存方法的一部分，其中写出临时文件，然后调用 FSExchangeObjectsCompat 以将新保存的临时文件与旧的“原始”文件交换。它保留了所有元数据、权限等。

我在 APFS 卷上的 High Sierra 上看到此功能失败，而在 HFS+ 卷上从未失败。不足为奇——其中许多调用已被弃用。

但是做同样事情的 Cocoa NSFileManager 方法是什么？

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2 回答 2

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你想要-[NSFileManager replaceItemAtURL:withItemAtURL:backupItemName:options:resultingItemURL:error:]。

于 2017-09-15T23:43:58.397 回答
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您可以使用较低级别的函数执行类似的操作。这是我编写的用于 10.12 之前的 SDK 的代码。如果您针对 10.12 SDK 或更高版本进行编译，则可以使其更简单一些，如果您的部署目标是 10.12 或更高版本，则更简单。

#ifndef RENAME_SWAP
#define RENAME_SWAP    0x00000002
#endif

/*!
    @function   ExchangeFiles

    @abstract   Given full paths to two files on the same volume,
                swap their contents.

    @discussion This is often part of a safe-save strategy.

    @param      inOldFile   Full path to a file.
    @param      inNewFile   Full path to a file.
    @result     0 if all went well, -1 otherwise.
*/
int ExchangeFiles( const char* inOldFile, const char* inNewFile )
{
    int result = -1;
    static dispatch_once_t sOnce = 0;
    static renameFuncType sRenameFunc = NULL;
    // Try to get a function pointer to renamex_np, which is available in OS 10.12 and later.
    dispatch_once( &sOnce,
        ^{
            sRenameFunc = (renameFuncType) dlsym( RTLD_DEFAULT, "renamex_np" );
        });

    // renamex_np is only available on OS 10.12 and later, and does not work on HFS+ volumes
    // but does work on APFS volumes.  Being the latest and greatest, we try it first.
    if (sRenameFunc != NULL)
    {
        result = (*sRenameFunc)( inOldFile, inNewFile, RENAME_SWAP );
    }

    if (result != 0)
    {
        // exchangedata is an older function that works on HFS+ but not APFS.
        result = exchangedata( inOldFile, inNewFile, 0 );
    }

    if (result != 0)
    {
        // Neither function worked, we must go old school.
        std::string nameTemplate( inOldFile );
        nameTemplate += "-swapXXXX";
        // Make a mutable copy of the template
        std::vector<char>   workPath( nameTemplate.size() + 1 );
        memcpy( &workPath[0], nameTemplate.c_str(), nameTemplate.size() + 1 );
        mktemp( &workPath[0] );
        std::string tempPath( &workPath[0] );

        // Make the old file have a temporary name
        result = rename( inOldFile, tempPath.c_str() );

        // Put the new file data under the old name.
        if (result == 0)
        {
            result = rename( inNewFile, inOldFile );
        }

        // Put the old data under the new name.
        if (result == 0)
        {
            result = rename( tempPath.c_str(), inNewFile );
        }
    }

    return result;
}
于 2017-09-15T21:09:35.227 回答