fix(printf): fix snprintf buffer termination

Fixes #7 (partly)

2 files changed, 66 insertions, 6 deletions

diff --git a/printf.c b/printf.c
index d9384f7..3cc7aa2 100644
--- a/printf.c
+++ b/printf.c
@@ -355,13 +355,13 @@ static size_t _vsnprintf(char* buffer, size_t buffer_len, const char* format, va
   unsigned int flags, width, precision, n;

   size_t idx = 0U;

 

-  while (idx < buffer_len) {

-    // end reached?

-    if (*format == (char)0) {

-      buffer[idx] = (char)0;

-      break;

-    }

+  // check if buffer is valid

+  if (!buffer) {

+    return 0U;

+  }

 

+  while ((idx < buffer_len) && *format)

+  {

     // format specifier?  %[flags][width][.precision][length]

     if (*format != '%') {

       // no

@@ -582,9 +582,16 @@ static size_t _vsnprintf(char* buffer, size_t buffer_len, const char* format, va
     }

   }

 

+  // termination

+  if (buffer_len > 0U) {

+    buffer[idx == buffer_len ? buffer_len - 1U : idx] = (char)0;

+  }

+

+  // return written chars without terminating \0

   return idx;

 }

 

+

 ///////////////////////////////////////////////////////////////////////////////

 

 int printf(const char* format, ...)

diff --git a/test/test_suite.cpp b/test/test_suite.cpp
index a8de789..e152ac7 100644
--- a/test/test_suite.cpp
+++ b/test/test_suite.cpp
@@ -1017,6 +1017,59 @@ TEST_CASE("unknown flag", "[]" ) {
 }

 

 

+TEST_CASE("buffer length", "[]" ) {

+  char buffer[100];

+  int ret;

+

+  // formatted length, this should return '4',

+  // but this feature is not implemented, returning 0

+  ret = test::snprintf(nullptr, 10, "%s", "Test");

+  REQUIRE(ret == 0);

+  ret = test::snprintf(nullptr, 0, "%s", "Test");

+  REQUIRE(ret == 0);

+

+  buffer[0] = (char)0xA5;

+  ret = test::snprintf(buffer, 0, "%s", "Test");

+  REQUIRE(buffer[0] == (char)0xA5);

+  REQUIRE(ret == 0);

+

+  buffer[0] = 0xCC;

+  test::snprintf(buffer, 1, "%s", "Test");

+  REQUIRE(buffer[0] == '\0');

+

+  test::snprintf(buffer, 2, "%s", "Hello");

+  REQUIRE(!strcmp(buffer, "H"));

+}

+

+

+TEST_CASE("ret value", "[]" ) {

+  char buffer[100] ;

+  int ret;

+

+  ret = test::snprintf(buffer, 6, "0%s", "1234");

+  REQUIRE(!strcmp(buffer, "01234"));

+  REQUIRE(ret == 5);

+

+  ret = test::snprintf(buffer, 6, "0%s", "12345");

+  REQUIRE(!strcmp(buffer, "01234"));

+  REQUIRE(ret == 6);  // '5' is truncated

+

+  ret = test::snprintf(buffer, 6, "0%s", "1234567");

+  REQUIRE(!strcmp(buffer, "01234"));

+  REQUIRE(ret == 6);  // '567' are truncated

+

+  ret = test::snprintf(buffer, 10, "hello, world");

+  REQUIRE(ret == 10);

+

+  ret = test::snprintf(buffer, 3, "%d", 10000);

+  REQUIRE(ret == 3);  // '000' are truncated

+  REQUIRE(strlen(buffer) == 2U);

+  REQUIRE(buffer[0] == '1');

+  REQUIRE(buffer[1] == '0');

+  REQUIRE(buffer[2] == '\0');

+}

+

+

 TEST_CASE("misc", "[]" ) {

   char buffer[100];