文件输入/输出C ++

Question

我想读取以下文件：其中以c开头的行表示注释，以p表示图形信息（无节点，无边缘），e表示边缘。

c   //Comments
c   //Comments
c   //Comments
p edge  50  654
e 4 1
e 5 3
e 5 4
e 6 2
e 6 3
... // 654 edges

我的想法是：

1. 逐行读取，直到一行的第一个索引== 'p';
2. 将矩阵初始化为节点大小，此处为50。
3. 读取amount_of_edges行数，将其保存到我的数据结构中（示例中为654行）。

我知道如何在Python中简单地做到这一点，但是我只是不知道从哪里开始使用c ++。

Answer 1

您可以尝试这样做：

ifstream file("myfile.txt");
string line;
while(true){
    getline(file, line);
    if(line[0]=='p') break;
 }
//now line contains a line starting with 'p' which contains the numbers
//that you need
stringstream data_from_line_with_p;
data_from_line_with_p << line;
//we have send the line to a stream, from which we can read to the variables
string p, edges;
int size_of_nodes, amount_of_edges;
//let's now assign these variables with data from the stream:
data_from_line_with_p >> p >> edges >> size_of_nodes >> amount_of_edges;

//now size_of_nodes and _amount_of_edges store the values read from this
//line and you can use them to build the structure that you want
//You also store here the word after 'p' in the variable 'edge' and you 
//can use it also if you need.

请记住添加一个用于使用stringstreams的标头： #include<sstream> 。