How to create a vector of array ( string [] ) in c++

Question

I have 2 string, from Sqlite3 , ColName and Value. I want to save each pair of values, i dont know the quantity of ColName/Value , so i use vector.

is there a way so i can create/push a ColName/Value to the vector of an array

code:

std::vector<std::string[3]> colNameAndValueList;//this doesnt work
string colName="ID";
string value="122001";
colNameAndValueList.push_back(std::string(colName,value));//im lost here

i dont know if i should use hash or struct, can anyone give me an advice?

thanks.

You can use a std::pair as in std::vector<std::pair<std::string, std::string>>. — huu
– huu, Commented May 1, 2015 at 18:39

Thomas Matthews · Accepted Answer · 2015-05-01 18:44:23Z

3

I recommend that you use a std::vector of structure:

struct Name_Value
{
  std::string name;
  std::string value;
};

typedef std::vector<Name_Value> Name_Value_Container;

This is a lot easier to read, understand, and implement.

answered May 1, 2015 at 18:44

Thomas Matthews

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Comments

huu · Accepted Answer · 2015-05-01 18:45:35Z

2

There are many ways to skin this cat. You can use std::pair and emplace_back to construct the pair in place when you're inserting values into your array:

std::vector<std::pair<std::string, std::string>> records;

std::string column = "hello";
std::string value = "world";

records.emplace_back(column, value); // Use existing strings
records.emplace_back("new", "value"); // Use c-string literals

for (auto& record : records) {
    std::cout << record.first << ": " << record.second << std::endl;
}

/*
 * Prints:
 * hello: world
 * new: value
 */

Here's a working example.

answered May 1, 2015 at 18:45

huu

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4 Comments

Luis Daniel Rubiera Over a year ago

Many thanks! , auto& would do the same as std::vector<std::pair<std::string, std::string> >::iterator it=records.begin(); it!= records.end();it++) ?

huu Over a year ago

In practice it's the same because both let you iterate through the vector. In code it isn't, auto& record is the actual std::pair<std::string, std::string>> object that lives inside the vector.

huu Over a year ago

You're correct, range based for loops are available starting with C++11.

Luis Daniel Rubiera Over a year ago

i will do it the old fashioned way, im working on a Mobile POS API that only allows C++98 , thanks :D

Vlad from Moscow · Accepted Answer · 2015-05-01 18:54:03Z

You can use a vector of objects of type std::pair. For example

std::vector<std::pair<std::string, std::string>> colNameAndValueList;

or a vector of objects of type std::array. For example

std::vector<std::array<std::string, 2>> colNameAndValueList;

Ordinary arrays do not have the copy assignment operator. So it is better not to use them in standard containers.

Here is a demonstrative program

#include <iostream>
#include <vector>
#include <array>


int main()
{
{
    std::vector<std::pair<std::string, std::string>> colNameAndValueList;

    colNameAndValueList.push_back( { "ID", "122001" } );

    for ( const auto &p : colNameAndValueList )
    {
        std::cout << p.first << ' ' << p.second << std::endl;
    }

}
{
    std::vector<std::array<std::string, 2>> colNameAndValueList;

    colNameAndValueList.push_back( { "ID", "122001" } );

    for ( const auto &a : colNameAndValueList )
    {
        for ( const auto &s : a ) std::cout << s << ' ';
        std::cout << std::endl;
    }

}

    return 0;
}

The program output is

ID 122001
ID 122001

Khaldor · Accepted Answer · 2015-05-01 18:46:37Z

0

To put in an answer, @huu has it right, use an

std::vector<std::pair<std::string, std::string>> myVector

    std::pair("ID", "122001") mypair;
    myVector.push_back(mypair);

Or a user defined struct.

// In your .h file
   struct myPair {
        std::string one;
        std::string two;
    };
// in your .c file
        myPair res;
        res.one = "ID";
        res.two = "122001";
        std::vector<myPair> myVector;
        myVector.push_back(res);

answered May 1, 2015 at 18:46

Khaldor

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