如何用7z源码，解压tar.gz压缩包。请用c++写一段代码实现

可以使用libarchive库来解压缩tar.gz压缩包，以下是使用7z源码解压缩的C++代码示例：

#include <iostream>
#include <cstring>
#include <cstdio>
#include "7z.h"
#include "7zAlloc.h"
#include "7zCrc.h"
#include "7zFile.h"
#include "7zVersion.h"

using namespace std;

int extract_tar_gz(const char* archive, const char* extract_path){
    CFileInStream archiveStream;
    CLookToRead lookStream;
    CSzArEx db;
    SRes res;
    UInt16 *temp = NULL;
    size_t tempSize = 0;
    int extractCount = 0;
    ISzAlloc allocImp;
    ISzAlloc allocTempImp;
    allocImp.Alloc = SzAlloc;
    allocImp.Free = SzFree;
    allocTempImp.Alloc = SzAllocTemp;
    allocTempImp.Free = SzFreeTemp;
    CrcGenerateTable();

    if (InFile_Open(&archiveStream.file, archive)){
        cout << "Error: Can not open file " << archive << endl;
        return -1;
    }

    FileInStream_CreateVTable(&archiveStream);
    LookToRead_CreateVTable(&lookStream, False);
    lookStream.realStream = &archiveStream.s;
    LookToRead_Init(&lookStream);

    SzArEx_Init(&db);
    res = SzArEx_Open(&db, &lookStream.s, &allocImp, &allocTempImp);
    if (res != SZ_OK){
        cout << "Error: Can not open archive " << archive << endl;
        return -1;
    }

    for (UInt32 i = 0; i < db.NumFiles; i++){
        size_t offset = 0;
        size_t outSizeProcessed = 0;
        const CSzFileItem* fileItem = db.Files + i;
        size_t len = SzArEx_GetFileNameUtf16(&db, i, NULL);
        if (len > tempSize){
            SzFree(NULL, temp);
            tempSize = len;
            temp = (UInt16*)SzAlloc(NULL, tempSize * sizeof(temp[0]));
        }
        SzArEx_GetFileNameUtf16(&db, i, temp);
        char* filename = (char*)malloc(len * 2 + 1);
        wcstombs(filename, (wchar_t*)temp, len * 2 + 1);

        if (fileItem->IsDir){
            continue;
        }

        if(strstr(filename, ".tar.gz") == NULL){
            continue;
        }

        char cmd[100];
        sprintf(cmd, "7z x -so \"%s\" 2>/dev/null | tar -xz -C \"%s\"", filename, extract_path);
        system(cmd);
        extractCount++;
        free(filename);
    }

    SzArEx_Free(&db, &allocImp);
    SzFree(NULL, temp);
    File_Close(&archiveStream.file);
    return extractCount;
}

int main(){
    extract_tar_gz("test.tar.gz", "extract_path");
    return 0;
}

代码中调用了系统的tar和7z命令，需要在Linux下运行。如果是在Windows下运行，需要修改命令行中的路径分隔符和/dev/null为nul。