clean build warnings

Chapter07/error_handling/CMakeLists.txt

@@ -115,6 +115,7 @@ add_executable(
   platform/src/system_stm32f0xx.c
   hal/uart/src/uart_stm32.cpp
   cstdlib_support/retarget.cpp
+  cstdlib_support/nosys_stubs.c
   ${MAIN_CPP_PATH}/${MAIN_CPP_FILE_NAME}
   )
 

Chapter07/error_handling/app/src/main_assert.cpp

@@ -42,7 +42,9 @@ int main()
 
     printf("Assert example\r\n");
     
-    const option opt = uint8_to_option(3);
+
+    // maybe_unused attribute will silence unused variable warning
+    [[maybe_unused]] const option opt = uint8_to_option(3);
 
     while(true)
     {

Chapter07/error_handling/cstdlib_support/nosys_stubs.c

@@ -0,0 +1,21 @@
+#include <sys/stat.h>
+#include <errno.h>
+#include <_ansi.h>
+#include <reent.h>
+
+/* Minimal implementation of _fstat_r */
+int _fstat_r(struct _reent *r, int file, struct stat *st) {
+    st->st_mode = S_IFCHR; /* Character device */
+    return 0;
+}
+
+/* Minimal implementation of _getpid_r */
+int _getpid_r(struct _reent *r) {
+    return 1; /* Return a dummy process ID */
+}
+
+/* Minimal implementation of _kill_r */
+int _kill_r(struct _reent *r, int pid, int sig) {
+    r->_errno = EINVAL;
+    return -1; /* Indicate failure */
+}