CODEWITHSUNDEEP
c++charstrcat
sdd
sdd

Reputation: 877

Short one: invalid conversion from char to const char*

code: 

void setup(){
 Serial.begin(19200);
 static char value [20] = "20:17:12";
 setSimTime(value);
}

void setSimTime(char* incoming){
  char dateTime[20];
  strcat(dateTime, "20");
  strcat(dateTime, incoming[0-1]);
  Serial.println(dateTime);
}

What is the right way to do this? Any help is appreciated

Upvotes: 1

Views: 644

Answers (2)

bjhend
bjhend

Reputation: 1713

The exact error message comes from the fact that incoming[0-1] is of type char, but strcat expects a const char* as second parameter, which is a pointer to a char.

The additional const is not a problem here, because non-const values can always be converted to const values.

See other answers/comments on the invalidity of incoming[0-1].

Upvotes: 1

Jonas
Jonas

Reputation: 7017

Using strcat(dateTime, incoming[0-1]);, where incoming[0-1] is the same as incoming[-1] causes undefined behavior. In fact incoming[-1] is the single character located at array index -1, this is the cause of the error, the compiler cannot convert a single character (char) into an char pointer (char*).

Instead use: 

strncat(dateTime, incoming, 2);

note the n in strncat. This will concatenate at most two characters from incoming to dateTime, and put a terminating null-character.

Extension

You can extend this to:

strncat(dateTime, incoming + n, l);

Where n is the starting index, i.e., zero before, and l is the max length to copy.

Example

So if you what to concatenate the characters with indexes 3 and 4 do:

strncat(dateTime, incoming + 3, 2);

Upvotes: 1

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