Handle printf error

.clang-tidy

@@ -2,4 +2,15 @@
 #
 # SPDX-License-Identifier: MIT
 
-WarningsAsErrors: '*'
+WarningsAsErrors: "*"
+
+Checks:
+  - clang-diagnostic-*,
+  - bugprone-*,
+  - cert-*,
+  - concurrency-*,
+  - misc-*,
+  - mpi-*,
+  - clang-analyzer-*,
+  # Disabled because `fprintf_s` is not available on all platforms.
+  - -clang-analyzer-security.insecureAPI.DeprecatedOrUnsafeBufferHandling

.github/workflows/ci.yml

@@ -5,6 +5,7 @@
 name: Project's CI
 on:
   workflow_dispatch:
+  pull_request:
   push:
     branches:
       - main

include/perfect-helloworld.h

@@ -7,6 +7,38 @@
 #pragma once
 
 /**
- * @brief Print "Hello, World!\n" and exit
+ * @brief
+ * Result of the library function.
  */
-void print_hello(void);
+enum PERFECT_HELLOWORLD_RESULT {
+    PERFECT_HELLOWORLD_RESULT_OK = 0,          //!< Success.
+    PERFECT_HELLOWORLD_RESULT_STDOUT_IO_ERROR, //!< Failure.
+};
+
+/**
+ * @brief
+ * Return a human-readable description of a PERFECT_HELLOWORLD_RESULT.
+ *
+ * @param res
+ * A result code returned by a function of this library.
+ *
+ * @return
+ * A pointer to a null-terminated, immutable string describing @p res.
+ *
+ * @note
+ * - The returned string has static storage duration and must not be freed or
+ *   modified by the caller.
+ *
+ * - This function is thread-safe.
+ *
+ * - For unknown or unsupported values of @p res, a generic "Unknown error" string
+ *   is returned.
+ */
+const char *perfect_helloworld_strerror(enum PERFECT_HELLOWORLD_RESULT res);
+
+/**
+ * @brief
+ * Print "Hello, World!\n".
+ */
+enum PERFECT_HELLOWORLD_RESULT
+perfect_helloworld_print_hello(void);

src/cli/main.c

@@ -2,11 +2,20 @@
 //
 // SPDX-License-Identifier: MIT
 
+#include <stdio.h>
 #include <stdlib.h>
 
 #include "perfect-helloworld.h"
 
 int main(void) {
-    print_hello();
+    enum PERFECT_HELLOWORLD_RESULT res = perfect_helloworld_print_hello();
+    if (res != PERFECT_HELLOWORLD_RESULT_OK) {
+        (void)fprintf(
+            stderr,
+            "perfect_helloworld_print_hello failed: %s\n",
+            perfect_helloworld_strerror(res));
+        return EXIT_FAILURE;
+    }
+
     return EXIT_SUCCESS;
 }

src/lib/perfect-helloworld.c

@@ -6,4 +6,22 @@
 
 #include "perfect-helloworld.h"
 
-void print_hello(void) { printf("Hello, World!\n"); }
+const char *
+perfect_helloworld_strerror(enum PERFECT_HELLOWORLD_RESULT res) {
+    switch (res) {
+    case PERFECT_HELLOWORLD_RESULT_OK:
+        return "Success";
+    case PERFECT_HELLOWORLD_RESULT_STDOUT_IO_ERROR:
+        return "I/O error while writing to standard output";
+    default:
+        return "Unknown perfect_helloworld error";
+    }
+}
+
+enum PERFECT_HELLOWORLD_RESULT perfect_helloworld_print_hello(void) {
+    if (fputs("Hello, World!\n", stdout) == EOF) {
+        return PERFECT_HELLOWORLD_RESULT_STDOUT_IO_ERROR;
+    }
+
+    return PERFECT_HELLOWORLD_RESULT_OK;
+}

tests/meson.build

@@ -6,10 +6,21 @@ if get_option('tests').enabled()
     unity = dependency('unity', required: get_option('tests'))
 
     test(
-        'test-perfect-helloworld',
+        'test-perfect-helloworld-print-hello-ok',
         executable(
-            'test-perfect-helloworld',
-            sources: files('test-perfect-helloworld.c'),
+            'test-perfect-helloworld-print-hello-ok',
+            sources: files('test-perfect-helloworld-print-hello-ok.c'),
+            link_with: lib,
+            dependencies: unity,
+            include_directories: inc,
+        ),
+    )
+
+    test(
+        'test-perfect-helloworld-print-hello-err',
+        executable(
+            'test-perfect-helloworld-print-hello-err',
+            sources: files('test-perfect-helloworld-print-hello-err.c'),
             link_with: lib,
             dependencies: unity,
             include_directories: inc,

tests/test-perfect-helloworld-print-hello-err.c

@@ -0,0 +1,31 @@
+// SPDX-FileCopyrightText: © 2026 Nikita Krasnov <nikita.nikita.krasnov@gmail.com>
+//
+// SPDX-License-Identifier: MIT
+
+#include <stdio.h>
+#include <unity.h>
+#include <unity_internals.h>
+
+#include "perfect-helloworld.h"
+
+void setUp(void) {
+    // set stuff up here
+}
+
+void tearDown(void) {
+    // clean stuff up here
+}
+
+static void test_perfect_helloworld_print_hello_err(void) {
+    (void)fclose(stdout);
+    enum PERFECT_HELLOWORLD_RESULT res = perfect_helloworld_print_hello();
+    TEST_ASSERT_EQUAL(PERFECT_HELLOWORLD_RESULT_STDOUT_IO_ERROR, res);
+}
+
+int main(void) {
+    UNITY_BEGIN();
+
+    RUN_TEST(test_perfect_helloworld_print_hello_err);
+
+    return UNITY_END();
+}

tests/test-perfect-helloworld.c → tests/test-perfect-helloworld-print-hello-ok.c

@@ -15,14 +15,15 @@ void tearDown(void) {
     // clean stuff up here
 }
 
-static void test_print_hello(void) {
-    print_hello();
+static void test_perfect_helloworld_print_hello_ok(void) {
+    enum PERFECT_HELLOWORLD_RESULT res = perfect_helloworld_print_hello();
+    TEST_ASSERT_EQUAL(PERFECT_HELLOWORLD_RESULT_OK, res);
 }
 
 int main(void) {
     UNITY_BEGIN();
 
-    RUN_TEST(test_print_hello);
+    RUN_TEST(test_perfect_helloworld_print_hello_ok);
 
     return UNITY_END();
 }