我正在开发一个应用程序，它将需要处理不同类型的文件。尽可能多的存档类型是好的。我选择了7zip.dll作为存档 worker 的引擎。但是有一个问题，有人知道如何将文件从存档解压缩到内存缓冲区吗？如我所见，7zip.dll仅支持解压缩到硬盘。另外，从内存缓冲区加载存档也将是一件好事。有没有人尝试做类似的事情？
最佳答案
不知道我是否完全了解您的需求(例如，您是否不需要磁盘上的解压缩文件？)。
我正在查看 LZMA SDK 9.20 及其 lzma.txt 自述文件，并且有很多暗示可以对内存进行解压缩-您可能只需要使用C API而不是C++接口(interface)。例如， check out 名为Single-call Decompressing的部分:
When to use: RAM->RAM decompressing
Compile files: LzmaDec.h + LzmaDec.c + Types.h
Compile defines: no defines
Memory Requirements:
- Input buffer: compressed size
- Output buffer: uncompressed size
- LZMA Internal Structures: state_size (16 KB for default settings)
此外，还有此功能:
SRes LzmaDec_DecodeToBuf(CLzmaDec *p, Byte *dest, SizeT *destLen,
const Byte *src, SizeT *srcLen, ELzmaFinishMode finishMode, ELzmaStatus *status);
您可以通过将归档文件进行内存映射来利用它们。据我所知，如果您的进程创建了一个具有独占访问权限的内存映射文件(因此没有其他进程可以访问它)并且不进行显式刷新，则对该文件的所有更改都将保留在内存中，直到映射被破坏或文件已关闭。或者，您可以只将存档内容加载到内存中。
为了完整起见，我将几个示例汇总为一个在Windows中使用内存映射的演示。
#include <stdio.h>
#include <time.h>
#include <Windows.h>
#include <WinNT.h>
// This demo will limit the file to 4KiB
#define FILE_SIZE_MAX_LOWER_DW 4096
#define FILE_SIZE_MAX_UPPER_DW 0
#define MAP_OFFSET_LOWER_DW 0
#define MAP_OFFSET_UPPER_DW 0
#define TEST_ITERATIONS 1000
#define INT16_SIZE 2
typedef short int int16;
// NOTE: This will not work for Windows less than XP or 2003 Server!
int main()
{
HANDLE hFile, hFileMapping;
PBYTE mapViewStartAddress;
// Note: with no explicit security attributes, the process needs to have
// the necessary rights (e.g. read, write) to this location.
LPCSTR path = "C:\\Users\\mcmlxxxvi\\Desktop\\test.dat";
// First, open a file handle.
hFile = CreateFile(path,
GENERIC_READ | GENERIC_WRITE, // The file is created with Read/Write permissions
FILE_SHARE_READ, // Set this to 0 for exclusive access
NULL, // Optional security attributes
CREATE_ALWAYS, // File is created if not found, overwritten otherwise
FILE_ATTRIBUTE_TEMPORARY, // This affects the caching behaviour
0); // Attributes template, can be left NULL
if ((hFile) == INVALID_HANDLE_VALUE)
{
fprintf(stderr, "Unable to open file");
return 1;
}
// Then, create a memory mapping for the opened file.
hFileMapping = CreateFileMapping(hFile, // Handle for an opened file
NULL, // Optional security attributes
PAGE_READWRITE, // File can be mapped for Read/Write access
FILE_SIZE_MAX_UPPER_DW, // Maximum file size split in DWORDs.
FILE_SIZE_MAX_LOWER_DW, // NOTE: I may have these two mixed up!
NULL); // Optional name
if (hFileMapping == 0)
{
CloseHandle(hFile);
fprintf(stderr, "Unable to open file for mapping.");
return 1;
}
// Next, map a view (a continuous portion of the file) to a memory region
// The view must start and end at an offset that is a multiple of
// the allocation granularity (roughly speaking, the machine page size).
mapViewStartAddress = (PBYTE)MapViewOfFile(hFileMapping, // Handle to a memory-mapped file
FILE_MAP_READ | FILE_MAP_WRITE, // Maps the view for Read/Write access
MAP_OFFSET_UPPER_DW, // Offset in the file from which
MAP_OFFSET_LOWER_DW, // the view starts, split in DWORDs.
FILE_SIZE_MAX_LOWER_DW); // Size of the view (here, entire file)
if (mapViewStartAddress == 0)
{
CloseHandle(hFileMapping);
CloseHandle(hFile);
fprintf(stderr, "Couldn't map a view of the file.");
return 1;
}
// This is where actual business stuff belongs.
// This example application does iterations of reading and writing
// random numbers for the entire length of the file.
int16 value;
errno_t result = 0;
srand((int)time(NULL));
for (int i = 0; i < TEST_ITERATIONS; i++)
{
// Write
for (int j = 0; j < FILE_SIZE_MAX_LOWER_DW / INT16_SIZE; j++)
{
value = rand();
result = memcpy_s(mapViewStartAddress + j * INT16_SIZE, INT16_SIZE, &value, INT16_SIZE);
if (result != 0)
{
CloseHandle(hFileMapping);
CloseHandle(hFile);
fprintf(stderr, "File write error during iteration #%d, error %d", i, GetLastError());
return 1;
}
}
// Read
SetFilePointer(hFileMapping, 0, 0, FILE_BEGIN);
for (int j = 0; j < FILE_SIZE_MAX_LOWER_DW / sizeof(int); j++)
{
result = memcpy_s(&value, INT16_SIZE, mapViewStartAddress + j * INT16_SIZE, INT16_SIZE);
if (result != 0)
{
CloseHandle(hFileMapping);
CloseHandle(hFile);
fprintf(stderr, "File read error during iteration #%d, error %d", i, GetLastError());
return 1;
}
}
}
// End business stuff
CloseHandle(hFileMapping);
CloseHandle(hFile);
return 0;
}
关于使用7zip.dll的C++，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/12040399/