CODEWITHSUNDEEP
cvariadic-functions
Akay
Akay

Reputation: 1132

Calling sprintf() under a variadic function in C

I want to write a quick printf() kinda function for an embedded board that I am working on where the output terminal is a serial port. I tried something like this:

int32_t printfDebugSerial(const char *format, ...)
{
  char tempBuff[256];
  memset(tempBuff, 0, sizeof tempBuff);

  va_list arg;
  int32_t done;
  va_start (arg, format);
  done = (int32_t)sprintf(tempBuff,format, arg);
  va_end (arg);

  HAL_sendToSerial((uint8_t*)tempBuff, strlen(tempBuff)); // writes bytes to serial port
  return done;
}

But the output that I got when I called it as follows:

printfDebugSerial("Hello = %u", 1234);

output:

Hello = 536929228

then called as:

printfDebugSerial("Hello = %f", 934.3245);

output:

Hello = 0.000000

Any help, what is wrong here?

Upvotes: 0

Views: 1041

Answers (1)

likle
likle

Reputation: 1797

You should use vsprintf instead of sprintf if you are forwarding va_list's:

int32_t printfDebugSerial(const char *format, ...)
{
  char tempBuff[256];
  memset(tempBuff, 0, sizeof tempBuff);

  va_list arg;
  int32_t done;
  va_start (arg, format);
  done = (int32_t)vsprintf(tempBuff,format, arg);
  va_end (arg);

  HAL_sendToSerial((uint8_t*)tempBuff, strlen(tempBuff)); // writes bytes to serial port
  return done;
}

Upvotes: 6

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