Merge pull request #4831 from fahhem/less_scanf

Remove excessive use of printf/scanf in mbed_fdopen/_open

Author: theotherjimmy

platform/mbed_retarget.cpp

@@ -228,10 +228,10 @@ extern "C" FILEHANDLE PREFIX(_open)(const char* name, int openmode) {
 
     FileHandle *res = NULL;
 
-    /* FILENAME: ":0x12345678" describes a FileHandle* */
+    /* FILENAME: ":(pointer)" describes a FileHandle* */
     if (name[0] == ':') {
         void *p;
-        std::sscanf(name, ":%p", &p);
+        memcpy(&p, name + 1, sizeof(p));
         res = (FileHandle*)p;
 
     /* FILENAME: "/file_system/file_name" */
@@ -826,8 +826,12 @@ void mbed_set_unbuffered_stream(std::FILE *_file) {
  */
 std::FILE *mbed_fdopen(FileHandle *fh, const char *mode)
 {
-    char buf[12]; /* :0x12345678 + null byte */
-    std::sprintf(buf, ":%p", fh);
+    // This is to avoid scanf(buf, ":%.4s", fh) and the bloat it brings.
+    char buf[1 + sizeof(fh)]; /* :(pointer) */
+    MBED_STATIC_ASSERT(sizeof(buf) == 5, "Pointers should be 4 bytes.");
+    buf[0] = ':';
+    memcpy(buf + 1, &fh, sizeof(fh));
+
     std::FILE *stream = std::fopen(buf, mode);
     /* newlib-nano doesn't appear to ever call _isatty itself, so
      * happily fully buffers an interactive stream. Deal with that here.