Convert an Arduino C++ String to an ANSI C string (char* array) using the String method .c_str() [duplicate] - string

Question

This question already has answers here:
How to convert a std::string to const char* or char*
(11 answers)
Closed 1 year ago.
because many posts about this problem are misleading or ambiguous, this is how it works, just for the record (tested):
How to convert an Arduino C++ String to an ANSI C string (char* array) using the String method .c_str()
String myString = "WLAN_123456789"; // Arduino String
char cbuffer[128]=""; // ANSI C string (char* array); adjust size appropriately
strcpy( cbuffer, myString.c_str() );
example (tested):
void setup() {
Serial.begin(115200);
delay(1000);
Serial.println();
String myString = "WLAN_123456789";
char cbuffer[128]="";
Serial.println(myString); // debug
strcpy( cbuffer, myString.c_str() );
Serial.println(cbuffer); // debug
}
void loop() {
}
PS:
the example is for variable Strings and for variable char arrays which are not constant, to be able to be assigned to repeatedly and arbitrarily
(also for constant strings optionally, too).

Answer 1

I know your intension is trying to share "best practise" of using String.c_str(), but I couldn't help to say that your "answer" is exactly the one that cause confusion, misleading or ambiguous that you said. If anyone find String.c_str() usage is misleading or ambiguous, it is because one probably does not read the c_str() on Arduino Reference, or fully understand the pointer well.
Converts the contents of a String as a C-style, null-terminated string. Note that this gives direct access to the internal String buffer and should be used with care. In particular, you should never modify the string through the pointer returned. When you modify the String object, or when it is destroyed, any pointer previously returned by c_str() becomes invalid and should not be used any longer.
String.c_str() return a pointer to char array (i.e. a array of char terminated with a '\0'), in another word const char* ptr = String.c_str() represented exactly what String.c_str() is about. Noticed that it is directly access to the buffer in the String object and you are not supposed to change it. So in most case, you use it like Serial.print(ptr). You only need to get a copy of it (as show in your strcpy) if you want to modified the content of your 'copy'.
To put it simply, if the char array (i.e. String.c_str()) is the banana you want to get from a jungle (i.e. the String object) which consists of the forest, the monkey and the whole nine yards, the String.c_str() point you directly to the banana, nothing more, nothing less.