Implement dynstr_substr.

2 files changed, 129 insertions, 0 deletions

diff --git a/dynstr.c b/dynstr.c
index ad03f7a..1d15a1c 100644
--- a/dynstr.c
+++ b/dynstr.c
@@ -141,3 +141,15 @@ size_t dynstr_memcpy(void *mem, Dynstr *dynstr, size_t offset, size_t size)
     return size;
 }
 
+Dynstr *dynstr_substr(Dynstr *dynstr, size_t offset, size_t size)
+{
+    if (offset >= dynstr->size) {
+        offset = 0;
+        size = 0;
+    } else if (size > dynstr->size - offset) {
+        size = dynstr->size - offset;
+    }
+    return new(dynstr->mem + offset, size, true);
+}
+
+
diff --git a/unittests.c b/unittests.c
index 6d0d2c9..a17686c 100644
--- a/unittests.c
+++ b/unittests.c
@@ -325,6 +325,116 @@ static int test_memcpy_copies_substring_ok(void)
 }
 
 
+static int test_copies_empty_substring_ok(void)
+{
+    Dynstr *dynstr;
+    Dynstr *sub;
+    size_t size;
+    char buf[1024];
+    
+    dynstr = dynstr_new_from_cstring("abcdef");
+    sub = dynstr_substr(dynstr, 1, 0);
+    size = dynstr_memcpy(buf, sub, 0, dynstr_len(sub));
+    FAIL_UNLESS_EQUAL(size, 0);
+    return true;
+}
+
+
+static int test_copies_single_byte_substring_ok(void)
+{
+    Dynstr *dynstr;
+    Dynstr *sub;
+    size_t size;
+    char buf[1024];
+    
+    dynstr = dynstr_new_from_cstring("abcdef");
+    sub = dynstr_substr(dynstr, 1, 1);
+    size = dynstr_memcpy(buf, sub, 0, dynstr_len(sub));
+    FAIL_UNLESS_EQUAL(size, 1);
+    FAIL_UNLESS_EQUAL(memcmp(buf, "b", 1), 0);
+    return true;
+}
+
+
+static int test_copies_middle_substring_ok(void)
+{
+    Dynstr *dynstr;
+    Dynstr *sub;
+    size_t size;
+    char buf[1024];
+    
+    dynstr = dynstr_new_from_cstring("abcdef");
+    sub = dynstr_substr(dynstr, 1, 4);
+    size = dynstr_memcpy(buf, sub, 0, dynstr_len(sub));
+    FAIL_UNLESS_EQUAL(size, 4);
+    FAIL_UNLESS_EQUAL(memcmp(buf, "bcde", 4), 0);
+    return true;
+}
+
+
+static int test_copies_initial_substring_ok(void)
+{
+    Dynstr *dynstr;
+    Dynstr *sub;
+    size_t size;
+    char buf[1024];
+    
+    dynstr = dynstr_new_from_cstring("abcdef");
+    sub = dynstr_substr(dynstr, 0, 5);
+    size = dynstr_memcpy(buf, sub, 0, dynstr_len(sub));
+    FAIL_UNLESS_EQUAL(size, 5);
+    FAIL_UNLESS_EQUAL(memcmp(buf, "abcde", 5), 0);
+    return true;
+}
+
+
+static int test_copies_final_substring_ok(void)
+{
+    Dynstr *dynstr;
+    Dynstr *sub;
+    size_t size;
+    char buf[1024];
+    
+    dynstr = dynstr_new_from_cstring("abcdef");
+    sub = dynstr_substr(dynstr, 1, 5);
+    size = dynstr_memcpy(buf, sub, 0, dynstr_len(sub));
+    FAIL_UNLESS_EQUAL(size, 5);
+    FAIL_UNLESS_EQUAL(memcmp(buf, "bcdef", 5), 0);
+    return true;
+}
+
+
+static int test_copies_empty_substring_when_offset_too_big(void)
+{
+    Dynstr *dynstr;
+    Dynstr *sub;
+    size_t size;
+    char buf[1024];
+    
+    dynstr = dynstr_new_from_cstring("abcdef");
+    sub = dynstr_substr(dynstr, 100, 1);
+    size = dynstr_memcpy(buf, sub, 0, dynstr_len(sub));
+    FAIL_UNLESS_EQUAL(size, 0);
+    return true;
+}
+
+
+static int test_copies_partial_substring_when_length_too_big(void)
+{
+    Dynstr *dynstr;
+    Dynstr *sub;
+    size_t size;
+    char buf[1024];
+    
+    dynstr = dynstr_new_from_cstring("abcdef");
+    sub = dynstr_substr(dynstr, 1, 6);
+    size = dynstr_memcpy(buf, sub, 0, dynstr_len(sub));
+    FAIL_UNLESS_EQUAL(size, 5);
+    FAIL_UNLESS_EQUAL(memcmp(buf, "bcdef", 5), 0);
+    return true;
+}
+
+
 static void setup(void)
 {
     dynstr_init();
@@ -367,6 +477,13 @@ static const struct test tests[] = {
     TEST(test_memcpy_truncates_if_copying_too_much),
     TEST(test_memcpy_copies_whole_string_ok),
     TEST(test_memcpy_copies_substring_ok),
+    TEST(test_copies_empty_substring_ok),
+    TEST(test_copies_single_byte_substring_ok),
+    TEST(test_copies_middle_substring_ok),
+    TEST(test_copies_initial_substring_ok),
+    TEST(test_copies_final_substring_ok),
+    TEST(test_copies_empty_substring_when_offset_too_big),
+    TEST(test_copies_partial_substring_when_length_too_big),
 };
 static const int num_tests = sizeof(tests) / sizeof(tests[0]);