Will this leak memory?

Projects Programming
10

As you said, either make the buffer static within the function and return a const char*

inline  const char* pascalsToMillibars(uint32_t pascals) {
  const size_t MBAR_STRLEN = 15;
  static char str[MBAR_STRLEN];
  snprintf (str, MBAR_STRLEN, "%4lu.%02lu mbar", pascals / 100ul, pascals % 100ul);
  return str;
}

void setup() {
  Serial.begin(115200); Serial.println();
  Serial.println(pascalsToMillibars(101325ul));
}

void loop() {}

or as suggested, let the caller provide the buffer and be responsible for the memory

inline char* pascalsToMillibars(char* str, const size_t len, uint32_t pascals) {
  snprintf (str, len, "%4lu.%02lu mbar", pascals / 100ul, pascals % 100ul);
  return str;
}

void setup() {
  const size_t MBAR_STRLEN = 15;
  char str[MBAR_STRLEN];
  Serial.begin(115200); Serial.println();
  Serial.println(pascalsToMillibars(str, MBAR_STRLEN, 101325ul));
}

void loop() {}