How to convert from vector to a number integer

Question

I have a vector with [ '6' '0' '0' '0' '0'] from a user inputting 60,000. I need an int 60000 so I can manipulate this number.

I'm new to c++ and programming in general. I read data/numbers from 60,000-3,500,000 from a serial port and I need an integer number, the only way I have successfully done this and printed it is through std::vector. I tried to do vector but it gives me funky numbers.

#include "SerialPort.h"
std::vector<char> rxBuf(15);
DWORD dwRead;
while (1) {
  dwRead = port.Read(rxBuf.data(), static_cast<DWORD>(rxBuf.size()));
  // this reads from a serial port and takes in data
  // rxBuf would hold a user inputted number in this case 60,000
  if (dwRead != 0) {
    for (unsigned i = 0; i < dwRead; ++i) {
      cout << rxBuf[i];
      // this prints out what rxBuf holds
    }
    // I need an int = 60,000 from my vector holding [ '6' '0' '0' '0 '0']
    int test = rxBuf[0 - dwRead];
    cout << test;
    // I tried this but it gives me the decimal equivalent of the character
    numbers
  }
}

I need an output of 60000 not in a vector but rather as a solid number, any help would be appreciated thanks.

Possible duplicate of [convert vector of char to an int](https://stackoverflow.com/questions/11240502/convert-vector-of-char-to-an-int) — Heath Raftery, Jul 08 '19 at 21:08
What did you expect from `rxBuf[0 - dwRead]`? There's a serious misunderstanding that needs to be corrected. Do you think that is an equivalent to Python's list slices? — LogicStuff, Jul 08 '19 at 21:09
What about skipping the `vector` and do `std::string rxBuf(15, 0);` and use that instead? — Ted Lyngmo, Jul 08 '19 at 21:11
Your issue really has little to do with vector, since a vector stores its data in contiguous memory, no different than an array of `char`. Thus the answer would be the same if you asked "how do I convert an array of char to `int`" — PaulMcKenzie, Jul 08 '19 at 21:30

Naslausky · Answer 1 · 2019-07-08T22:05:25.113

9

From this answer, you could do something like:

std::string str(rxBuf.begin(), rxBuf.end());

To convert your Vector to a String.

After that, you could use the std::stoi function:

int output = std::stoi(str);
    std::cout << output << "\n";

edited Jul 08 '19 at 22:05

answered Jul 08 '19 at 21:08

Naslausky

3,443
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2

Note: if the vector string still is null terminated you can use `std::stoi(rxBuf.data())` directly. – DColt Jul 08 '19 at 21:13

score 5 · Answer 2 · answered Jul 08 '19 at 21:07

5

Loop over the elements of an std::vector and construct an int from them:

std::vector<char> chars = {'6', '0', '0', '0', '0'};

int number = 0;

for (char c : chars) {
    number *= 10;
    int to_int = c - '0'; // convert character number to its numeric representation
    number += to_int;
}

std::cout << number / 2; // prints 30000

answered Jul 08 '19 at 21:07

Fureeish

12,533
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Not as eloquent as some other answers, but gets the job done. – Jul 08 '19 at 21:15
I like this more than other answers because it does not rely on `std::string` nor `std::stoi` - no memory allocation or unnecessary checking. Although I would prefer `std::uint32_t` instead of `int`. – Quimby Jul 08 '19 at 21:24

score 3 · Answer 3 · answered Jul 08 '19 at 21:11

3

Use a std::string to build your string:

std::string istr;
char c = 'o';
istr.push_back(c);

Then use std::stoi to convert to integer; std::stoi

int i = std::stoi(istr);

answered Jul 08 '19 at 21:11

Demolishun

1,592
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score 3 · Answer 4 · answered Jul 08 '19 at 21:22

C++17 added the std::from_chars function that can do what you want without modifying or copying the input vector:

std::vector<char> chars = {'6', '0', '0', '0', '0'};
int number;
auto [p, ec] = std::from_chars(chars.data(), chars.data() + chars.size(), number);
if (ec != std::errc{}) {
    std::cerr << "unable to parse number\n";
} else {
    std::cout << "number is " << number << '\n';
}

Live Demo

score 2 · Answer 5 · answered Jul 08 '19 at 21:27

To minimize the need for temporary variables, use a std::string with the appropriate length as a buffer.

#include "SerialPort.h"
#include <string>

std::string rxBuf(15, '\0');
DWORD dwRead;

while (1) {
    dwRead = port.Read(rxBuf.data(), static_cast<DWORD>(rxBuf.size()));

    if (dwRead != 0) {
        rxBuf[dwRead] = '\0'; // set null terminator
        int test = std::stoi(rxBuf);
        cout << test;
    }
}

How to convert from vector to a number integer

5 Answers5