feat(printf): added new oprintf() function

Write formatted output directly to given output function

README.md

@@ -50,6 +50,9 @@ int printf(const char* format, ...);
 int sprintf(char* buffer, const char* format, ...);
 int snprintf(char* buffer, size_t count, const char* format, ...);
 int vsnprintf(char* buffer, size_t count, const char* format, va_list va);
+
+// write to output function (instead of buffer)
+int oprintf(void (*out)(char character), const char* format, ...);
 ```
 
 

printf.c

@@ -101,6 +101,14 @@ static inline void _out_char(char character, char* buffer, size_t idx, size_t ma
 }
 
 
+// internal output function wrapper
+static inline void _out_fct(char character, char* buffer, size_t idx, size_t maxlen)
+{
+  (void)idx; (void)maxlen;
+  ((void (*)(char character))buffer)(character);  // buffer is the output fct pointer
+}
+
+
 // internal strlen
 // \return The length of the string (excluding the terminating 0)
 static inline unsigned int _strlen(const char* str)
@@ -674,7 +682,17 @@ int snprintf(char* buffer, size_t count, const char* format, ...)
 }
 
 
-inline int vsnprintf(char* buffer, size_t count, const char* format, va_list va)
+int vsnprintf(char* buffer, size_t count, const char* format, va_list va)
 {
   return _vsnprintf(_out_buffer, buffer, count, format, va);
 }
+
+
+int oprintf(void (*out)(char character), const char* format, ...)
+{
+  va_list va;
+  va_start(va, format);
+  const int ret = _vsnprintf(_out_fct, (char*)out, (size_t)-1, format, va);
+  va_end(va);
+  return ret;
+}

printf.h

@@ -60,7 +60,7 @@ int printf(const char* format, ...);
 
 /**
  * Tiny sprintf implementation
- * Due to security reasons (buffer overflow) YOU SHOULD CONSIDER USING SNPRINTF INSTEAD!
+ * Due to security reasons (buffer overflow) YOU SHOULD CONSIDER USING (V)SNPRINTF INSTEAD!
  * \param buffer A pointer to the buffer where to store the formatted string. MUST be big enough to store the output!
  * \param format A string that specifies the format of the output
  * \return The number of characters that are WRITTEN into the buffer, not counting the terminating null character
@@ -80,6 +80,16 @@ int  snprintf(char* buffer, size_t count, const char* format, ...);
 int vsnprintf(char* buffer, size_t count, const char* format, va_list va);
 
 
+/**
+ * printf with output function
+ * You may use this as dynamic alternative to printf() with its fixed _putchar() output
+ * \param out An output function which takes one character
+ * \param format A string that specifies the format of the output
+ * \return The number of characters that are sent to the output function, not counting the terminating null character
+ */
+int oprintf(void (*out)(char character), const char* format, ...);
+
+
 #ifdef __cplusplus
 }
 #endif

test/test_suite.cpp

@@ -50,8 +50,6 @@ void test::_putchar(char character)
 
 
 TEST_CASE("printf", "[]" ) {
-  char buffer[100];
-
   printf_idx = 0U;
   memset(printf_buffer, 0xCC, 100U);
   REQUIRE(test::printf("% d", 4232) == 5);
@@ -59,6 +57,14 @@ TEST_CASE("printf", "[]" ) {
 }
 
 
+TEST_CASE("oprintf", "[]" ) {
+  printf_idx = 0U;
+  memset(printf_buffer, 0xCC, 100U);
+  test::oprintf(&test::_putchar, "This is a test of %X", 0x12EFU);
+  REQUIRE(!strcmp(printf_buffer, "This is a test of 12EF"));
+}
+
+
 TEST_CASE("snprintf", "[]" ) {
   char buffer[100];