從.txt文件中讀取浮點數

Question

如何從.txt文件中讀取浮點數。 根據每行開頭的名稱，我想讀取不同數量的坐標。 浮標由“空間”分隔。

示例： triangle 1.2 -2.4 3.0

結果應為： float x = 1.2 / float y = -2.4 / float z = 3.0

該文件有更多的線條與不同的形狀，可能會更復雜，但我想如果我知道如何做其中一個我可以自己做其他人。

我的代碼到目前為止：

#include <iostream>

#include <fstream>

using namespace std;

int main(void)

{

    ifstream source;                    // build a read-Stream

    source.open("text.txt", ios_base::in);  // open data

    if (!source)  {                     // if it does not work
        cerr << "Can't open Data!\n";
    }
    else {                              // if it worked 
        char c;
        source.get(c);                  // get first character

        if(c == 't'){                   // if c is 't' read in 3 floats
            float x;
            float y;
            float z;
            while(c != ' '){            // go to the next space
            source.get(c);
            }
            //TO DO ??????              // but now I don't know how to read the floats          
        }
        else if(c == 'r'){              // only two floats needed
            float x;
            float y;
            while(c != ' '){            // go to the next space
            source.get(c);
            }
            //TO DO ??????
        }                                
        else if(c == 'p'){              // only one float needed
            float x;
            while(c != ' '){            // go to the next space
            source.get(c);
            }
            //TODO ???????
        }
        else{
            cerr << "Unknown shape!\n";
        }
    }   
 return 0;
}

Answer 1

為什么不以通常的方式使用C ++流而不是所有這些getc瘋狂：

#include <sstream>
#include <string>

for(std::string line; std::getline(source, line); )   //read stream line by line
{
    std::istringstream in(line);      //make a stream for the line itself

    std::string type;
    in >> type;                  //and read the first whitespace-separated token

    if(type == "triangle")       //and check its value
    {
        float x, y, z;
        in >> x >> y >> z;       //now read the whitespace-separated floats
    }
    else if(...)
        ...
    else
        ...
}

Answer 2

這應該工作：

string shapeName;
source >> shapeName;
if (shapeName[0] == 't') {
    float a,b,c;
    source >> a;
    source >> b;
    source >> c;
}