Converting Strings to Doubles in C

In C , converting a string to a double can be achieved using the std::istringstream and std::stod functions.

#include 

double string_to_double(const std::string& s) {
  std::istringstream iss(s);
  double x;
  if (!(iss >> x)) {
    return 0;  // Return 0 for non-numerical strings
  }
  return x;
}

Here's how this function works:

1. Create an std::istringstream object iss from the input string s.
2. Use the >> operator to extract a double value from iss.
3. If the extraction is successful, return the double value.
4. If the extraction fails (e.g., the string is not numerical), return 0.

Note that this function cannot fully distinguish all allowed string representations of zero from non-numerical strings. For example, it considers all the following strings as zero:

"0"
"0."
"0.0"

Here are some test cases to demonstrate the usage of the string_to_double function:

#include 

int main() {
  assert(0.5 == string_to_double("0.5"));
  assert(0.5 == string_to_double("0.5 "));
  assert(0.5 == string_to_double(" 0.5"));
  assert(0.5 == string_to_double("0.5a"));

  assert(0 == string_to_double("0"));
  assert(0 == string_to_double("0."));
  assert(0 == string_to_double("0.0"));
  assert(0 == string_to_double("foobar"));

  return 0;
}