How can I read the numbers in a char array as integers? - c++

Question

I want to pass dimension parameters of a matrix class as a char array, I can get the number of dimensions by counting the number of commas written in the parameters but I cant seem to read the numbers in a char as integers.
When I try to convert from char to int I get huge unrelated numbers. How can I read the numbers in a char array as integers?
template <class T>
matrix <T>::matrix (char * dimensions)
{
int nod = 0;
for(int i=0;dimensions[i];i++)
{
if (dimensions[i] == ',') nod++;
}
Number_of_dimensions = nod+1;
//...
}

Answer 1

You can use the following idea, illustrated with a rough pseudo-code snipper:
std::string s = "1234,4556";
//While you still have a string to parse
while (s.length()) {
//Use a comma to delimit a token
std::string delimiter = ",";
//Find the position of the comma or the end of the string
unsigned int comma_pos = s.find(delimiter);
//Find the sub-string before the comma
std::string token = s.substr(0, comma_pos); // token is "1234"
//Find your int
int i = std::stoi(token);
//"Eat" the token, continue
s.erase(0, comma_pos+1);
}
This is a particularly rough example, but the core idea is there: use std::string::substr() to find your sub-string with a comma delimiter, then convert the token to an int.
You also might want to consider looking for several delimiters, such as '\n'.

Answer 2

Split() function splits string by delimiter. In our case delimiter is comma. The number of elements is dimension. Than we convert each element to number using std::stringstream (C++98, or std::stoi in C++11).
#include <iostream>
#include <sstream>
#include <vector>
#include <string>
std::vector<std::string> Split(const std::string &s, char delim)
{
std::vector<std::string> elems;
std::stringstream ss(s);
std::string item;
while (std::getline(ss, item, delim))
elems.push_back(item);
return elems;
}
std::vector<int> GetDim(char *dimensions)
{
std::vector<std::string> dim_str = Split(dimensions, ',');
std::vector<int> elems(dim_str.size());
for (size_t i = 0; i < dim_str.size(); ++i) {
std::stringstream ss(dim_str[i]);
ss >> elems.at(i);
}
return elems;
}
int main() {
std::string s = "1234,4556";
std::vector<int> d = GetDim(&*s.begin());
std::cout << "Dimensions: " << d.size() << std::endl;
std::cout << "Values: ";
for (size_t i = 0; i < d.size(); ++i) {
std::cout << d[i] << " ";
}
std::cout << std::endl;
return 0;
}
I suggest you not to use pointer as arguments. Use std::string or std::vector instead. Do not forget const qualifier. So GetDim() can be:
std::vector<int> GetDim(const std::string& dimensions)
{
std::vector<std::string> dim_str = Split(dimensions, ',');
std::vector<int> elems(dim_str.size());
for (size_t i = 0; i < dim_str.size(); ++i) {
std::stringstream ss(dim_str[i]);
ss >> elems.at(i);
}
return elems;
}