C和C++的文件操作

C

    FILE *fp;
    double sum = 0,x;
    int m;
    fp = fopen("in.txt","r");
    fscanf(fp,"%d",&m);
    for(int i = 1; i <= m; i++)
    {
        fscanf(fp,"%lf",&x);
        sum += x;
    }
    fclose(fp);
    if(m == 0)
        return ;

    fp = fopen("out.txt","w"); //w写整个文件，覆盖以前数据，a追加到文件末
    fprintf(fp,"%f\n",sum/m);
    fclose(fp);

 

C++

    fstream in,out;//和cin和cout类似，对文件操作
    in.open("in.txt",ios::in);
    if(in == NULL) return;

    out.open("out.txt",ios::out);
    if(!out) return;

    int m;
    double sum = 0,x;
    in>>m;
    for(int i = 1; i <= m; i++)
    {
        in>>x;
        sum+=x;
    }
    out<<sum/m<<endl;

    in.close();
    out.close();

 

使用read和write函数

    fstream in,out;
    in.open("in.txt", ios::in);
    out.open("out.txt", ios::out)
    if(in == NULL) return 0;
    memset(cnt, 0 ,sizeof cnt);
    if(in.good())
    {
        in.read(buf,sizeof buf);
        num = in.gcount();
        out.write(buf, num);
    }