How to Convert String to Vector [duplicate] - c++

Question

This question already has answers here:
Right way to split an std::string into a vector<string>
(12 answers)
Closed 7 years ago.
I'm writing 2 programs, the first program has an array of integers
vector<int> v = {10, 200, 3000, 40000};
Then it converts the vector into string
int i;
stringstream sw;
string stringword;
for (i=0;i<v.size();i++)
{
sw << v[i] << ',';
}
stringword = sw.str();
cout << "Vector in string : "<< stringword << endl;
And then write it in a file
ofstream myfile;
myfile.open ("writtentext");
myfile << stringword;
myfile.close();
The output :
Vector in string : 10,200,3000,40000
The second program will read the file, convert the string back to integer, and then push it back to vector.
The code :
string stringword;
ifstream myfile;
myfile.open ("writtentext");
getline (myfile,stringword);
cout << "Read From File = " << stringword << endl;
cout << "Convert back to vector = " ;
for (int i=0;i<stringword.length();i++)
{
if (stringword.find(','))
{
int value;
istringstream (stringword) >> value;
v.push_back(value);
stringword.erase(0, stringword.find(','));
}
}
for (int j=0;j<v.size();j++)
{
cout << v.at(j) << " " ;
}
The problem is, it can only convert and push back the first element, the rest is erased. Here is the output :
Read From File = 10,200,3000,40000,
Convert back to vector = 10
What did I do wrong? Thanks

Answer 1

There's problem with your for loop
Consider this:
while(1) //Use a while loop, "i" isn't doing anything for you
{
//if comman not found find return string::npos
if (stringword.find(',')!=std::string::npos)
{
int value;
istringstream (stringword) >> value;
v.push_back(value);
//Erase all element including comma
stringword.erase(0, stringword.find(',')+1);
}
else
break; //Come out of loop
}
Instead, just use std::stringstream to read back from file
std::stringstream ss(stringword);
int value;
while (ss >> value)
{
v.push_back(value);
if (ss.peek() == ',')
ss.ignore();
}
for (int j=0;j<v.size();j++) //Fix variables
{
cout << v.at(j) << " " ; // Can use simply v[j]
}

Answer 2

for (int j=0;j<v.size();i++)
{
cout << v.at(i) << " " ;
}
should be
for (int j=0;j<v.size();j++)
{
cout << v.at(j) << " " ;
}
i is not declared in the for loop

Answer 3

You can skip the string conversion. All stream can handle int types.
std::vector<int> to output:
#include <iostream>
#include <iterator>
#include <vector>
int main() {
std::vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
std::ostream_iterator<int> output_iterator(std::cout, ",");
std::copy(v.begin(), v.end(), output_iterator);
}
input to std::vector<int>:
#include <iostream>
#include <vector>
#include <sstream>
using namespace std;
int main() {
std::vector<int> v;
int value;
std::string line;
while(getline(cin, line, ',')) {
std::stringstream ss(line);
ss >> value
v.push_back(value);
}
typedef std::vector<int>::iterator iter;
iter end = v.end();
for(iter it = v.begin(); it != end; ++it) {
std::cout << *it << endl;
}
}

Answer 4

this is only a mistake you did:
for (int j=0;j<v.size();i++)
{
cout << v.at(i) << " " ;
}
but the implement is too inefficient here:
for (int i=0;i<stringword.length();i++)
{
if (stringword.find(','))
{
int value;
istringstream (stringword) >> value;
v.push_back(value);
stringword.erase(0, stringword.find(','));
}
}
you may do like this, just a suggestion:
#include <iostream>
#include <string>
#include <vector>
#include <stdlib.h>
int ConvertStringToInt(const std::string &str, std::vector<int> &ints)
{
int count_int = 0;
std::string string_int;
size_t start = 0;
size_t end = 0;
while ((end = str.find(',', start)) != std::string::npos)
{
string_int.assign(str, start, end - start);
ints.push_back(atoi(string_int.c_str()));
start = end + 1;
++count_int;
}
if (start != str.size())
{
ints.push_back(atoi(str.c_str() + start));
++count_int;
}
return count_int;
}
int main(int argc, char *const argv[])
{
std::vector<int> ints;
std::string str = "123,456,789 ";
std::cout << ConvertStringToInt(str, ints) << std::endl;
for (size_t i = 0; i != ints.size(); ++i)
{
std::cout << ints[i] << std::endl;
}
return 0;
}

Answer 5

You can make your programs simpler:
#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <vector>
// output
int main()
{
// my compiler doesn't support initializer lists yet :(
std::vector<int> v(4);
v[0] = 10;
v[1] = 200;
v[2] = 3000;
v[3] = 40000;
std::ofstream fout("mytestfile.txt");
std::copy(v.begin(), v.end(), std::ostream_iterator<int>(fout, ","));
fout.close();
return 0;
}
// input
struct int_reader : std::ctype<char>
{
int_reader() : std::ctype<char>(get_table()) {}
static std::ctype_base::mask const* get_table()
{
static std::vector<std::ctype_base::mask> rc(table_size, std::ctype_base::mask());
rc[','] = std::ctype_base::space;
rc['\n'] = std::ctype_base::space;
return &rc[0];
}
};
int main()
{
std::vector<int> v;
std::ifstream fin("mytestfile.txt", std::ifstream::in);
fin.imbue(std::locale(std::locale(), new int_reader()));
std::copy(std::istream_iterator<int>(fin), std::istream_iterator<int>(), std::back_inserter<std::vector<int>>(v));
fin.close();
std::cout << "You read in: ";
std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));
return 0;
}

Answer 6

Though this is handcrafted instead of using std::stringstream, I find it quite easy to understand.
std::vector<std::string> StringToVector (const std::string s,
const char token)
{
std::vector<std::string> v;
size_t posLast = 0, pos = 0;
while((pos = s.find(token, pos)) != std::string::npos)
{
if(s[pos] != s[posLast])
v.push_back(s.substr(posLast, pos - posLast));
posLast = ++pos;
}
if(s[posLast] != 0) // If there is no terminating token found
v.push_back(s.substr(posLast));
return v;
}
Demo with various test cases.