fstream和stringstream之间的转换_c++ stringstream和fstream之间的转换

#include <fstream>
#include <sstream>

    const char* filepath = "C:/test.txt";
    ifstream in(filepath);
    if(in.bad())
    {
        printf("open file '%d' failed!", filepath);
        return;
    }
    stringstream ss;

    ss << in.rdbuf();
    string str(ss.str());
    printf(str.c_str());
    
    in.close();
 

void RegexSearch::LoadStreamFromFile( char** buffer,const char* filepath )
{
    FILE* pFile = NULL;
    int err = ::fopen_s(&pFile, filepath, "rb");
    if(0 != err)
    {
        printf("open file '%s' failed!", filepath);
        return;
    }
    unsigned int length = 0;
    int growSize = 512;
    while(!feof(pFile))
    {
        char* temp = (char*)calloc(length + growSize, sizeof(char));
        //将之前已读取的字节流拷贝到新的已扩容的动态数组中
        memcpy( temp, *buffer, length );
        if(*buffer)
            free(*buffer);
        *buffer = temp;
        //每次读取固定大小growSize长度个字符，并拼接到*buffer指向的字符串尾部
        fread((*buffer) + length, sizeof(char), growSize, pFile);
        length += growSize;
    }
    fclose(pFile);
}