Getting an error in C++ using vector and struct

Question

What is the error in this code:

    #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

struct symtab{
  string name;
  string location;
};
vector<symtab> symtab_details;

bool search_symtab(string s){

  if (find (symtab_details.begin(), symtab_details.end(), s)!=symtab_details.end()) return true;
  return false;
}


int main() {

    bool get = search_symtab("ADD");
    return 0;
}

I am getting the following error:

usr/include/c++/4.8.2/bits/stl_algo.h:166:17: error: no match for ‘operator==’ (operand types are ‘symtab’ and ‘const std::basic_string’) if (*__first == __val)

The find function tries to find a symtab structure in your vector. Learn about lambda expressions and std::find_if for one way of solving your problem. — Some programmer dude
– Some programmer dude, Commented Mar 31, 2018 at 21:33
overload operator== in your symtab class so that it can be compared to a const std::string & — FBergo
– FBergo, Commented Mar 31, 2018 at 21:35
The error is quite clear. If you don't understand why it's an error, please read more about operator overloading before opening questions about it, as it is a pretty fundamental feature of the language. — underscore_d
– underscore_d, Commented Apr 1, 2018 at 9:19

R Sahu · Accepted Answer · 2018-03-31 21:37:36Z

8

You are trying to find a std::string, "ADD", in a std::vector<symtab>. Of course that won't work.

What you need is std::find_if.

auto it = std::find_if(symtab_details.begin(),
                       symtab_details.end(),
                       [&s](symtab const& item) { return item.name == s; });
return  (it != symtab_details.end());

answered Mar 31, 2018 at 21:37

R Sahu

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5 Comments

R Sahu Over a year ago

@Debian_yadav, you need to compile using a C++11 compiler. E.g. if you use g++, you can use -std=c++11 in the command line to compile your program as a C++11 program.

Prvt_Yadav Over a year ago

I am using g++ compiler

R Sahu Over a year ago

@Debian_yadav, use -std=c++11 then.

Prvt_Yadav Over a year ago

But I am having linker problem in gcc

R Sahu Over a year ago

@Debian_yadav, that was a typo on my part. Use g++ -std=c++11.

Pete Becker · Accepted Answer · 2018-03-31 21:33:18Z

3

The code is searching for an object of type symtab that matches an object of type std::string. So you have to provide a comparison operator to tell whether a particular symtab object is equal to a particular std::string object. You need

bool operator==(const symtab&, const std::string&);

If you read the error message carefully that's what it's telling you.

answered Mar 31, 2018 at 21:33

Pete Becker

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