c++: ifstrinfg记录

头文件

#include 
#include 
#include 

获取文件大小

std::size_t getFileSize1(const std::string& filename)
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return -1;
    }
    std::filebuf* pbuf = in.rdbuf();
    std::size_t size = pbuf->pubseekoff (0,in.end,in.in);
    in.close();
    return size;
}

long getFileSize(const std::string& filename)
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return -1;
    }
    std::streampos  begin = in.tellg();
    in.seekg(0,std::ios::end);
    auto end  = in.tellg();
    in.close();

    return (end-begin);
}

c语言

long cgetFileSize(const std::string& filename)
{
    FILE* fp  = fopen(filename.c_str(),"r");
    if(!fp){
        return -1;
    }
    fseek(fp,0,SEEK_END);
    long lSize = ftell(fp);
    fclose(fp);
    return lSize;
}

读取所有

bool readAll(const std::string& filename,std::string& out)
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return false;
    }
    std::istreambuf_iterator<char> begin{in},end;
    out.append(begin,end);
    in.close();
    return true;
}

https://cplusplus.com/reference/fstream/ifstream/rdbuf/

char* readAll(const std::string& filename)
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return nullptr;
    }
    std::streampos  begin = in.tellg();
    in.seekg(0,std::ios::end);
    auto end  = in.tellg();
    auto nFilesize = (end-begin);
    char* buf =new(std::nothrow) char[nFilesize];
    if(!buf){
        return nullptr;
    }
    in.seekg(0,std::ios::beg);
    in.read(buf,nFilesize);
    in.close();
    return buf;
}

char* readAll1(const std::string& filename)
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return nullptr;
    }
    std::filebuf* pbuf = in.rdbuf();

    // get file size using buffer's members
    std::size_t size = pbuf->pubseekoff (0,in.end,in.in);
    pbuf->pubseekpos (0,in.in);

    // allocate memory to contain file data
    char* buffer=new(std::nothrow) char[size];
    if(!buffer){
        return nullptr;
    }
    // get file data
    pbuf->sgetn (buffer,size);

    // write content to stdout
    std::cout.write (buffer,size);

    in.close();

    return buffer;
}

读取字节

void readChar(const std::string& filename,bool (*cb)(char))
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return;
    }
    while(in.good()){
        char ch = in.get();
        if(cb(ch)){
            break;
        }
    };
    in.close();
}

读取字节测试

  readChar("main.cpp",[](char ch)->bool{
        std::cout<<ch;
        return false;
    });

读取行

void readLine(const std::string& filename,bool (*cb)(char*))
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return;
    }
    char* str = new(std::nothrow) char[1024];
    while(in.good()){
        in.getline(str,1024);
        if(cb(str)){
            break;
        }
    };
    delete []str;
    in.close();
}

读取字符串

输出单个单词，即以空格为分割

void readString(const std::string& filename,bool (*cb)(const std::string& str))
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return;
    }
    std::string str;
    while(in >> str){
        if(cb(str)){
            break;
        }
    };

    in.close();
}

读取int

void readInt(const std::string& filename,bool (*cb)(int value))
{
    std::ifstream in{filename};
    if(!in.is_open()){
        return;
    }
    int value;
    while(in >> value){
        if(cb(value)){
            break;
        }
    };

    in.close();
}

测试

文件内容

123  456

读取

 readInt("D:\\1.txt",[](int value)->bool{
        std::cout<<value<<std::endl;
        return false;
    });

输出

123
456