Converting int[] to String in C++

Question

I have a string defined as std::string header = "00110033"; now I need the string to hold the byte values of the digits as if its constructed like this

char data_bytes[] = { 0, 0, 1, 1, 0, 0, 3, 3};
std::string header = new std::string(data_bytes, 8).c_str());

I converted the initial string to int array using atoi. Now i'm not sure how to make the string out of it. Let me know if there is any better approach.

syntax of 2nd line isn't correct. Also, what's the intention of the new here? — Karl von Moor
– Karl von Moor, Commented Mar 7, 2011 at 17:42
Why do you need to do this? What are you going to do if the array contains a value that is not between 0 and 9? — Karl Knechtel
– Karl Knechtel, Commented Mar 7, 2011 at 18:03
It's inefficient (due to copying) and a memory leak (due to new without storing the pointer for a corresponding delete) to say std::string header = (new std::string(data_bytes, 8))->c_str(); (or whatever it is you meant). You can just say std::string header(data_bytes, 8); instead. — Jon Purdy
– Jon Purdy, Commented Mar 7, 2011 at 18:18

Optimus Prime · Accepted Answer · 2015-04-11 15:20:13Z

4

you could write a little function

string int_array_to_string(int int_array[], int size_of_array) {
  string returnstring = "";
  for (int temp = 0; temp < size_of_array; temp++)
    returnstring += itoa(int_array[temp]);
  return returnstring;
}

^untested!

a slightly different approach

string int_array_to_string(int int_array[], int size_of_array) {
  ostringstream oss("");
  for (int temp = 0; temp < size_of_array; temp++)
    oss << int_array[temp];
  return oss.str();
}

edited Apr 11, 2015 at 15:20

Optimus Prime

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answered Mar 7, 2011 at 17:43

ultifinitus

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3 Comments

UmmaGumma Over a year ago

@ultifinitus atoi converts string to int, while you need to convert int to string. You need to use itoa, which is not standard function, so probably best solution is to convert int to character by adding '0' (see my solution). You also can use lexical cast: boost::lexical_cast<std::string>(int_array[temp]);

RageD Over a year ago

Use std::stringstream instead, it's safer.

ultifinitus Over a year ago

Oh good heavens, I'll revamp it, it was a 5 second function geez! =)

Sarfaraz Nawaz · Accepted Answer · 2011-03-07 18:30:24Z

2

Do this:

  char data_bytes[] = { '0', '0', '1', '1', '0', '0', '3', '3', '\0'};
  std::string header(data_bytes, 8);

Or maybe, you want to do this:

  std::stringstream s;
  s << data_bytes;
  std::string header = s.str();

Demo at ideone : http://ideone.com/RzrYY

EDIT:

Last \0 in data_bytes is necessary. Also see this interesting output here: http://ideone.com/aYtlL

PS: I didn't know this before, thanks to Ashot I came to know this difference by experimenting!

edited Mar 7, 2011 at 18:30

answered Mar 7, 2011 at 17:44

Sarfaraz Nawaz

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11 Comments

Nick Rolando Over a year ago

You can't store ints in a char array

UmmaGumma Over a year ago

@Nawaz -1 data_bytes is not ending with '\0' so you can't print it. + In both cases your string will not be equal to string("00110033");

Nick Rolando Over a year ago

You won't get the results you expect

Sarfaraz Nawaz Over a year ago

@Ashot: I saw that, and fixed it as well. @Nicklamort: The problem is fixed. However, it was nothing to do with "storing ints ina char".

UmmaGumma Over a year ago

@Nawaz remove last '\0' in data_bytes. Your string is ending with double '\0' now :) See this topic stackoverflow.com/questions/4711449/….

|

UmmaGumma · Accepted Answer · 2011-03-07 17:46:14Z

1

 char data_bytes[] = { 0, 0, 1, 1, 0, 0, 3, 3};
  std::string str;
 for(int i =0;i<sizeof(data_bytes);++i)
      str.push_back('0'+data_bytes[i]);

answered Mar 7, 2011 at 17:46

UmmaGumma

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Comments

Mark B · Accepted Answer · 2011-03-07 17:48:40Z

1

Assuming you're using a "fairly normal" system where the numeric values of '0' to '9' are consecutive, you can just iterate over each element and subtract '0':

for(int i = 0; i < header.size(); ++i)
{
    header[i] -= '0';
}

answered Mar 7, 2011 at 17:48

Mark B

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2 Comments

Eugen Constantin Dinca Over a year ago

Shouldn't you be adding instead of substracting?

Mark B Over a year ago

@Eugen Constantin Dinca The OP has a string like "00111" and wants it to be translated to one with those actual byte values, for example "00111" -> "\000\000\001\001\001". Thus you subtract.

Eugen Constantin Dinca · Accepted Answer · 2011-03-07 17:53:30Z

1

You can do this:

std::string header( data_bytes, data_bytes + sizeof( data_bytes ) );
std::transform( header.begin(), header.end(), header.begin(), 
     std::bind1st( std::plus< char >(), '0' ) );

answered Mar 7, 2011 at 17:53

Eugen Constantin Dinca

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Comments

Pe Dro · Accepted Answer · 2019-11-03 08:20:13Z

0

If integ[] is the integer array, and s is the final string we wish to obtain,

string s="";

for(auto i=0;i<integ.size()-1; ++i)
    s += to_string(ans[i]); 

cout<<s<<endl;

answered Nov 3, 2019 at 8:20

Pe Dro

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