The easiest way to read formatted input in C++?

问题:

Is there any way to read a formatted string like this, for example :48754+7812=Abcs.

Let's say I have three stringz X,Y and Z, and I want

X = 48754 
Y = 7812
Z = Abcs

The size of the two numbers and the length of the string may vary, so I dont want to use substring() or anything like that.

Is it possible to give C++ a parameter like this

":#####..+####..=SSS.."

so it knows directly what's going on?

回答1:

A possibility is boost::split(), which allows the specification of multiple delimiters and does not require prior knowledge of the size of the input:

#include <iostream>
#include <vector>
#include <string>

#include <boost/algorithm/string.hpp>
#include <boost/algorithm/string/split.hpp>

int main()
{
    std::vector<std::string> tokens;
    std::string s(":48754+7812=Abcs");
    boost::split(tokens, s, boost::is_any_of(":+="));

    // "48754" == tokens[0]
    // "7812"  == tokens[1]
    // "Abcs"  == tokens[2]

    return 0;
}

Or, using sscanf():

#include <iostream>
#include <cstdio>

int main()
{
    const char* s = ":48754+7812=Abcs";
    int X, Y;
    char Z[100];

    if (3 == std::sscanf(s, ":%d+%d=%99s", &X, &Y, Z))
    {
        std::cout << "X=" << X << "\n";
        std::cout << "Y=" << Y << "\n";
        std::cout << "Z=" << Z << "\n";
    }

    return 0;
}

However, the limitiation here is that the maximum length of the string (Z) must be decided before parsing the input.

回答2:

#include <iostream>
#include <sstream>

int main(int argc, char **argv) {
  std::string str = ":12341+414112=absca";
  std::stringstream ss(str);
  int v1, v2; 
  char col, op, eq; 
  std::string var;
  ss >> col >> v1 >> op >> v2 >> eq >> var;
  std::cout << v1 << " " << v2 << " " << var << std::endl;
  return 0;
}

回答3:

You can use scanf. It is not overly C++ - ish, but it does the trick with remarkably few lines of code:

char a[101], b[111], c[121];
sscanf(":48754+7812=Abcs", ":%100[^+]+%110[^=]=%120s", a, b, c);
string sa(a), sb(b), sc(c);
cout << sa << "-" << sb  << "-" << sc << endl;

The idea is to specify the characters accepted by the strings that you read using a very limited regular expression syntax. In this case, the first string is read up to the plus, and the second string is read up to the equals sign.

回答4:

for example.

#include <boost/regex.hpp>
#include <iostream>

int main()
{
   boost::regex re("\":(\\d+)\\+(\\d+)=(.+)\"");
   std::string example = "\":48754+7812=Abcs\"";
   boost::smatch match;
   if (boost::regex_match(example, match, re))
   {
      std::cout << "f number: " << match[1] << " s number: " << match[2] << " string: " << match[3]
      << std::endl;
   }
   else
   {
      std::cout << "not match" << std::endl;
   }
}

and second variant, work only with string.

#include <string>
#include <iostream>

int main()
{
   std::string s = "\":48754+7812=Abcs\"";
   std::string::size_type idx = s.find(":");
   std::string::size_type end_first = s.find("+", idx + 1);
   std::string f_number = s.substr(idx + 1, end_first - (idx + 1));
   std::cout << f_number << std::endl;
   std::string::size_type end_second = s.find("=", end_first + 1);
   std::string s_number = s.substr(end_first + 1, end_second - (end_first + 1));
   std::cout << s_number << std::endl;
   std::string::size_type string_end = s.find("\"", end_second);
   std::string str = s.substr(end_second + 1, string_end - (end_second + 1));
   std::cout << str << std::endl;
}