How to Determine if a C String Represents an Integer?

Determining if a C String Represents an Integer

Problem:

When working with user input, you may encounter strings that contain a mix of words and numbers. If you want to isolate only the words, you need a method to distinguish them from numbers.

Solution:

One approach to verifying if a string represents an integer is to employ the strtol() function. To simplify its usage, you can incorporate it into a custom function:

<code class="cpp">inline bool isInteger(const std::string & s)
{
   if(s.empty() || ((!isdigit(s[0])) &amp;&amp; (s[0] != '-') &amp;&amp; (s[0] != '+'))) return false;

   char * p;
   strtol(s.c_str(), &amp;p, 10);

   return (*p == 0);
}</code>

Explanation:

strtol() parses a string as a numerical value, stopping at the first non-numerical character. By supplying a pointer to a character variable (p), it indicates the position of the first invalid character. If p points to the end of the string, all characters were successfully converted, indicating that the string is an integer.

Usage:

Within your main function, you can integrate this function as follows:

<code class="cpp">int main () {
  stringstream ss (stringstream::in | stringstream::out);
  string word;
  string str;
  getline(cin,str);
  ss<<str;
  while(ss>>word)
    {
      if(isInteger(word))
        continue;
      cout<<word<<endl;
    }
}</code>

This will output words that are not integers while ignoring numerical inputs.

The above is the detailed content of How to Determine if a C String Represents an Integer?. For more information, please follow other related articles on the PHP Chinese website!