How can we change const char* arguments during the application running?

[kamotsuru]

I want to change the value of some const char* arguments of syslog() constructor during the application running.

The following is some parts of my code.
Inside loop(), I copied a string derived from the serial input to std::string object. If I create const char* variable "testapp" and put it to syslog.appName() like the following, it works.
However, If I put the copied std::string object with the same string "testapp" replacing with the commented out // line, the library sends other value than "testapp". Even if I put the same string "testapp" multiple times, it changes. It seems to refer the different memory address's value.

This may be c++ programing issue, but could you let me know how to solve this if possible?

//global scope
Syslog syslog(udpClient, server, SYSLOG_PORT, "esp32", LOG_KERN);

void loop() {
...
if (Serial.available() > 0) {
String str = Serial.readStringUntil('\n');
if (str[0] == 'R') {
...
} else if (str[0] == 'A') {
std::string para = myOffset(str, 2);
const char* param = "testapp";
Serial.println(strcmp(para.c_str(), param));
// syslog.appName((const char*)(para.c_str()));
syslog.appName(param);
}
}
...
syslog.logf(LOG_INFO, "%s %d %f %f", d.getAddress().toString().c_str(), id, current, voltage);
}

std::string myOffset (String string, int offset) {
std::string para = "";
for (int i = offset; i < string.length(); i++) {
para += string[i];
}
return para;
}