C++-compatible regex replace with only glibc regex.h

regexReplace.cpp

#include <regex.h>

std::string regexReplace(
    const std::string& inStr,
    const std::string& regexStr,
    const std::string& repl) {
  int ret = 0;
  // Create expr
  regex_t regex;
  if ((ret = regcomp(&regex, regexStr.c_str(), REG_EXTENDED))) {
    throw std::runtime_error("regcomp: Cannot compile regular expression.");
  }
  // In string to buffer
  const char* inCSTr = inStr.c_str();
  const std::string::size_type inSize = inStr.size();
  char* inBuffer = new char[inSize + 1];
  memcpy(inBuffer, inCSTr, inSize + 1);
  // Running output buffer
  std::string out;
  // Replace
  regmatch_t pmatch[1];
  char* curr = inBuffer;
  while ((ret = regexec(&regex, curr, 0, NULL, 0)) != REG_NOMATCH) {
    if (ret || regexec(&regex, curr, 1, pmatch, 0)) {
      throw std::runtime_error("regexec: Error finding regex matches.");
    };
    regoff_t startOffset = pmatch[0].rm_so;
    regoff_t endOffset = pmatch[0].rm_eo;
    // Append unmatched substring and repl
    out += std::string(curr, startOffset);
    out += repl;
    curr += endOffset;
  }
  // Remaining unmatched chars
  out += std::string(curr);
  regfree(&regex);
  delete[] inBuffer;
  return out;
}