Implement dynstr_byte_at.

2 files changed, 33 insertions, 1 deletions

diff --git a/dynstr.c b/dynstr.c
index b3daa9e..777ed28 100644
--- a/dynstr.c
+++ b/dynstr.c
@@ -9,7 +9,7 @@
 
 
 struct Dynstr {
-    const char *mem;
+    const unsigned char *mem;
     size_t size;
     bool dynamic;
 };
@@ -197,3 +197,11 @@ Dynstr *dynstr_cat(Dynstr *dynstr, ...)
     return result;
 }
 
+
+int dynstr_byte_at(Dynstr *dynstr, size_t offset)
+{
+    if (offset >= dynstr->size)
+        return -1;
+    return dynstr->mem[offset];
+}
+
diff --git a/unittests.c b/unittests.c
index e6caa0a..fcd740b 100644
--- a/unittests.c
+++ b/unittests.c
@@ -518,6 +518,28 @@ static int test_cat_returns_NULL_for_second_malloc_failure(void)
 }
 
 
+static int test_byteat_reports_correct_character(void)
+{
+    Dynstr *dynstr;
+    
+    dynstr = dynstr_new_from_cstring("abc");
+    FAIL_UNLESS_EQUAL(dynstr_byte_at(dynstr, 1), 'b');
+    dynstr_free(dynstr);
+    return true;
+}
+
+
+static int test_byteat_reports_error_for_too_large_offset(void)
+{
+    Dynstr *dynstr;
+    
+    dynstr = dynstr_new_from_cstring("abc");
+    FAIL_UNLESS_EQUAL(dynstr_byte_at(dynstr, 1024), -1);
+    dynstr_free(dynstr);
+    return true;
+}
+
+
 static void setup(void)
 {
     dynstr_init();
@@ -570,6 +592,8 @@ static const struct test tests[] = {
     TEST(test_cats_ok),
     TEST(test_cat_returns_NULL_for_first_malloc_failure),
     TEST(test_cat_returns_NULL_for_second_malloc_failure),
+    TEST(test_byteat_reports_correct_character),
+    TEST(test_byteat_reports_error_for_too_large_offset),
 };
 static const int num_tests = sizeof(tests) / sizeof(tests[0]);