function template
<string>

std::stoi

int stoi (const string&  str, size_t* idx = 0, int base = 10);
int stoi (const wstring& str, size_t* idx = 0, int base = 10);
Convert string to integer
Parses str interpreting its content as an integral number of the specified base, which is returned as an int value.

If idx is not a null pointer, the function also sets the value of idx to the position of the first character in str after the number.

The function uses strtol (or wcstol) to perform the conversion (see strtol for more details on the process).

Parameters

str
String object with the representation of an integral number.
idx
Pointer to an object of type size_t, whose value is set by the function to position of the next character in str after the numerical value.
This parameter can also be a null pointer, in which case it is not used.
base
Numerical base (radix) that determines the valid characters and their interpretation.
If this is 0, the base used is determined by the format in the sequence (see strtol for details). Notice that by default this argument is 10, not 0.

Return Value

On success, the function returns the converted integral number as an int value.

Example

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// stoi example
#include <iostream>   // std::cout
#include <string>     // std::string, std::stoi

int main ()
{
  std::string str_dec = "2001, A Space Odyssey";
  std::string str_hex = "40c3";
  std::string str_bin = "-10010110001";
  std::string str_auto = "0x7f";

  std::string::size_type sz;   // alias of size_t

  int i_dec = std::stoi (str_dec,&sz);
  int i_hex = std::stoi (str_hex,nullptr,16);
  int i_bin = std::stoi (str_bin,nullptr,2);
  int i_auto = std::stoi (str_auto,nullptr,0);

  std::cout << str_dec << ": " << i_dec << " and [" << str_dec.substr(sz) << "]\n";
  std::cout << str_hex << ": " << i_hex << '\n';
  std::cout << str_bin << ": " << i_bin << '\n';
  std::cout << str_auto << ": " << i_auto << '\n';

  return 0;
}


Output:

2001, A Space Odyssey: 2001 and [, A Space Odyssey]
40c3:  16579
-10010110001: -1201
0x7f: 127

Complexity

Unspecified, but generally linear in the number of characters interpreted.

Data races

Modifies the value pointed by idx (if not zero).

Exceptions

If no conversion could be performed, an invalid_argument exception is thrown.
If the value read is out of the range of representable values by an int, an out_of_range exception is thrown.

An invalid idx causes undefined behavior.

See also

stol
Convert string to long int (function template )
stoul
Convert string to unsigned integer (function template )
strtol
Convert string to long integer (function )