feat(printf): added PRINTF_OVERRIDE_LIBC support

Fixes #16

README.md

@@ -160,6 +160,8 @@ int length = sprintf(NULL, "Hello, world"); // length is set to 12
 
 | Name | Default value | Description |
 |------|---------------|-------------|
+| PRINTF_INCLUDE_CONFIG_H  | undefined | Define this as compiler switch (e.g. `gcc -DPRINTF_INCLUDE_CONFIG_H`) to include a "printf_config.h" definition file |
+| PRINTF_OVERRIDE_LIBC     | undefined | Define this to override the LIBC function declarations by using `printf_()` instead of `printf()` directly |
 | PRINTF_NTOA_BUFFER_SIZE  | 32        | ntoa (integer) conversion buffer size. This must be big enough to hold one converted numeric number _including_ leading zeros, normally 32 is a sufficient value. Created on the stack |
 | PRINTF_FTOA_BUFFER_SIZE  | 32        | ftoa (float) conversion buffer size. This must be big enough to hold one converted float number _including_ leading zeros, normally 32 is a sufficient value. Created on the stack |
 | PRINTF_SUPPORT_FLOAT     | defined   | Define this to enable floating point (%f) support |

printf.c

@@ -699,8 +699,11 @@ static int _vsnprintf(out_fct_type out, char* buffer, const size_t maxlen, const
 
 ///////////////////////////////////////////////////////////////////////////////
 
-
+#ifndef PRINTF_OVERRIDE_LIBC
 int printf(const char* format, ...)
+#else
+int printf_(const char* format, ...)
+#endif
 {
   va_list va;
   va_start(va, format);
@@ -711,7 +714,11 @@ int printf(const char* format, ...)
 }
 
 
+#ifndef PRINTF_OVERRIDE_LIBC
 int sprintf(char* buffer, const char* format, ...)
+#else
+int sprintf_(char* buffer, const char* format, ...)
+#endif
 {
   va_list va;
   va_start(va, format);
@@ -721,7 +728,11 @@ int sprintf(char* buffer, const char* format, ...)
 }
 
 
+#ifndef PRINTF_OVERRIDE_LIBC
 int snprintf(char* buffer, size_t count, const char* format, ...)
+#else
+int snprintf_(char* buffer, size_t count, const char* format, ...)
+#endif
 {
   va_list va;
   va_start(va, format);
@@ -731,13 +742,21 @@ int snprintf(char* buffer, size_t count, const char* format, ...)
 }
 
 
+#ifndef PRINTF_OVERRIDE_LIBC
 int vsnprintf(char* buffer, size_t count, const char* format, va_list va)
+#else
+int vsnprintf_(char* buffer, size_t count, const char* format, va_list va)
+#endif
 {
   return _vsnprintf(_out_buffer, buffer, count, format, va);
 }
 
 
+#ifndef PRINTF_OVERRIDE_LIBC
 int fctprintf(void (*out)(char character, void* arg), void* arg, const char* format, ...)
+#else
+int fctprintf_(void (*out)(char character, void* arg), void* arg, const char* format, ...)
+#endif
 {
   va_list va;
   va_start(va, format);

printf.h

@@ -25,7 +25,7 @@
 // \brief Tiny printf, sprintf and snprintf implementation, optimized for speed on
 //        embedded systems with a very limited resources.
 //        Use this instead of bloated standard/newlib printf.
-//        These routines are thread safe and reentrant!
+//        These routines are thread safe and reentrant.
 //
 ///////////////////////////////////////////////////////////////////////////////
 
@@ -56,6 +56,12 @@ extern "C" {
 void _putchar(char character);
 
 
+// if PRINTF_OVERRIDE_LIBC is is defined, the regular printf() API is overridden by macro defines
+// and internal underscore-appended functions like printf_() are used to avoid conflicts with
+// LIBC defined printf() functions.
+// default: undefined
+#ifndef PRINTF_OVERRIDE_LIBC
+
 /**
  * Tiny printf implementation
  * You have to implement _putchar if you use printf()
@@ -97,6 +103,23 @@ int vsnprintf(char* buffer, size_t count, const char* format, va_list va);
  */
 int fctprintf(void (*out)(char character, void* arg), void* arg, const char* format, ...);
 
+#else   // PRINTF_OVERRIDE_LIBC
+
+// override the LIBC defined function names
+#define printf    printf_
+#define sprintf   sprintf_
+#define snprintf  snprintf_
+#define vsnprintf vsnprintf_
+#define fctprintf fctprintf_
+
+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);
+int fctprintf_(void (*out)(char character, void* arg), void* arg, const char* format, ...);
+
+#endif  // PRINTF_OVERRIDE_LIBC
+
 
 #ifdef __cplusplus
 }