Stuck in the jungel of types and conversions.. int+ const char*

Projects Programming
1

Hi,
i´m in the beginning in getting familar with C and struggle with data types.
My example is pretty simple:
I want to retrieve the current date and want to extract a const char* cch_timeFullDate which contains for example: "Samstag, 3. Dezember".
I´m struggeling in getting a single variable of const char* and int combined:

// ** TIME
const char* cch_timeMonthNames[] = {"Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember"};
const char* cch_timeWeekdayNames[] = {"Sonntag", "Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag"};
char* ch_timeMonthName;
char* ch_timeWeekdayName;
const char* cch_timeFullDate;
int int_timeMinute;
int int_timeHour;
int int_timeDay;
int int_timeMonth;
int int_timeWeekday;


void initTime(){
  struct tm timeinfo;
  Serial.println("Setting up time");
  configTzTime("CET-1CEST,M3.5.0/02,M10.5.0/03", "ptbtime1.ptb.de"); 
  if(!getLocalTime(&timeinfo)){
    Serial.println("  Failed to obtain time");
    return;
  }
  Serial.println(&timeinfo, "%A, %d %B %Y %H:%M:%S");
}
boolean getCurrentTime(){
  struct tm timeinfo;
  Serial.println("Get current time");
  if(!getLocalTime(&timeinfo)){
    Serial.println("  Failed to obtain time");
    return false;
  }
  int_timeMinute = timeinfo.tm_min;
  int_timeHour = timeinfo.tm_hour;
  int_timeDay = timeinfo.tm_mday;
  int_timeWeekday = timeinfo.tm_wday;
  int_timeMonth = timeinfo.tm_mon;
  ch_timeMonthName = cch_timeMonthNames[int_timeMonth];
  ch_timeWeekdayName = cch_timeWeekdayNames[int_timeWeekday];
  cch_timeFullDate = printf("%s, %d. %s", ch_timeWeekdayName, int_timeDay, ch_timeMonthName);
  return true;
}

Any help is appreciated

2

Drop the "*" below and and perform a standard character array definition:

For example:

const char cch_timeMonthNames[][10]= {"Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember"};
const char cch_timeWeekdayNames[][12] = {"Sonntag", "Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag"};

Please post an error messages, using code tags and explain where you are having the difficulty.

3

To combine you can use sprintf


const char * dayOfWeek   = "Monday";
const char * month       = "December";
uint8_t day = 12;
char result[30];

void setup() 
{
  Serial.begin(115200);  
  
  sprintf(result, "The date is %s %d %s", dayOfWeek, day, month);
  Serial.println(result);
}

void loop() 
{}

10:51:21.910 -> The date is Monday 12 December
4

i tried the following:

// ** TIME
const char cch_timeMonthNames[][10] = {"Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember"};
const char cch_timeWeekdayNames[][12] = {"Sonntag", "Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag"};

boolean getCurrentTime(){
  struct tm timeinfo;
  Serial.println("Get current time");
  if(!getLocalTime(&timeinfo)){
    Serial.println("  Failed to obtain time");
    return false;
  }
  int_timeMinute = timeinfo.tm_min;
  int_timeHour = timeinfo.tm_hour;
  int_timeDay = timeinfo.tm_mday;
  int_timeWeekday = timeinfo.tm_wday;
  int_timeMonth = timeinfo.tm_mon;
  ch_timeMonthName = cch_timeMonthNames[int_timeMonth];
  ch_timeWeekdayName = cch_timeWeekdayNames[int_timeWeekday];
  cch_timeFullDate = printf("%s, %d. %s", ch_timeWeekdayName, int_timeDay, ch_timeMonthName);
  return true;
}

This leads to an error:

In function 'boolean getCurrentTime()':
xxxxx:58:54: error: invalid conversion from 'const char*' to 'char*' [-fpermissive]
ch_timeMonthName = cch_timeMonthNames[int_timeMonth];

5

You can't assign a value to a pointer like that.

There is no need to use any pointers in your application. Just use sprintf() to move the value into the printable ASCII C-string that you want.

Try this:

void setup() {
  Serial.begin(115200);
  while(!Serial);
  const char cch_timeMonthNames[][10] = {"Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember"};
  char buf[40];
  sprintf(buf, "Monat: %s", cch_timeMonthNames[1]);
  Serial.println(buf);
}

void loop() {}

or use strcpy() to copy the string wherever you like.

6

Just do as I showed above...

7

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