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

Question

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?

Answer 1

#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;
}

Answer 2

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.

Answer 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.

Answer 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;
}