strtol method

int strtol(String nptr, { List<String>? endptr, int radix = 10, })

Converts the string nptr to an int.

Trims leading whitespace, handles optional signs, stops at the first invalid character, and autodetects the radix (base) if radix is 0 (e.g. 0x for 16). If endptr is provided, endptr[0] is set to the unparsed remainder of the string.

Implementation

int strtol(String nptr, {List<String>? endptr, int radix = 10}) {
  if (nptr.isEmpty) {
    if (endptr != null && endptr.isNotEmpty) endptr[0] = nptr;
    return 0;
  }
  int i = 0;

  // Skip whitespace
  while (i < nptr.length) {
    int c = nptr.codeUnitAt(i);
    if (c == 32 || (c >= 9 && c <= 13)) {
      i++;
    } else {
      break;
    }
  }
  if (i >= nptr.length) {
    if (endptr != null && endptr.isNotEmpty) endptr[0] = nptr;
    return 0;
  }

  int start = i;
  bool negative = false;
  int c = nptr.codeUnitAt(i);
  if (c == 45) { // '-'
    negative = true;
    i++;
  } else if (c == 43) { // '+'
    i++;
  }

  if (i >= nptr.length) {
    if (endptr != null && endptr.isNotEmpty) endptr[0] = nptr;
    return 0;
  }

  int actualRadix = radix;
  if (actualRadix == 0) {
    if (nptr.codeUnitAt(i) == 48) { // '0'
      if (i + 1 < nptr.length && (nptr.codeUnitAt(i + 1) == 120 || nptr.codeUnitAt(i + 1) == 88)) {
        actualRadix = 16;
        i += 2;
      } else {
        actualRadix = 8;
      }
    } else {
      actualRadix = 10;
    }
  } else if (actualRadix == 16) {
    if (nptr.codeUnitAt(i) == 48 && i + 1 < nptr.length && (nptr.codeUnitAt(i + 1) == 120 || nptr.codeUnitAt(i + 1) == 88)) {
      i += 2;
    }
  }

  int numStart = i;

  // Scan digits
  while (i < nptr.length) {
    c = nptr.codeUnitAt(i);
    int digit = -1;
    if (c >= 48 && c <= 57) { digit = c - 48; }
    else if (c >= 65 && c <= 90) { digit = c - 65 + 10; }
    else if (c >= 97 && c <= 122) { digit = c - 97 + 10; }

    if (digit == -1 || digit >= actualRadix) break;
    i++;
  }

  if (i == numStart) {
    if (numStart > start && (nptr.codeUnitAt(numStart - 1) == 120 || nptr.codeUnitAt(numStart - 1) == 88)) {
       i = numStart - 1;
       if (endptr != null && endptr.isNotEmpty) {
         endptr[0] = nptr.substring(i);
       }
       return 0;
    }

    if (endptr != null && endptr.isNotEmpty) endptr[0] = nptr;
    return 0;
  }

  if (endptr != null && endptr.isNotEmpty) {
    endptr[0] = nptr.substring(i);
  }

  String valStr = nptr.substring(numStart, i);
  String fullStr = (negative ? "-" : "") + valStr;

  return int.tryParse(fullStr, radix: actualRadix) ?? 0;
}