Fixed various bugs and added usage for String data type

Makefile

@@ -1,7 +1,7 @@
 CC = gcc
 CFLAGS = -Wall -Wextra -Werror -pedantic-errors -fstack-protector-strong \
 	-fsanitize=address -fsanitize=undefined -fstack-clash-protection \
-	-Wwrite-strings -g -std=c99
+	-fdiagnostics-color=always -Wwrite-strings -g -std=c99
 
 BENCH_FLAGS = -Wall -Wextra -Werror -O3
 

src/string.c

@@ -22,7 +22,7 @@ static inline int utf8_char_len(unsigned char byte) {
     if ((byte & 0x80) == 0x00) return 1;
     if ((byte & 0xE0) == 0xC0) return 2;
     if ((byte & 0xF0) == 0xE0) return 3;
-    if ((byte & 0xF0) == 0xE0) return 4;
+    if ((byte & 0xF8) == 0xF0) return 4;
 
     return -1;
 }
@@ -285,7 +285,7 @@ string_result_t string_concat(const string_t *x, const string_t *y) {
         return result;
     }
 
-    memcpy(buf, x->data, y->byte_size);
+    memcpy(buf, x->data, x->byte_size);
     memcpy(buf + x->byte_size, y->data, y->byte_size);
     buf[new_size] = '\0';
     result = string_new(buf);
@@ -400,7 +400,7 @@ string_result_t string_substring(const string_t *haystack, const string_t *needl
  *
  *  Gets symbol indexed by @position from @str
  *
- *  Returns a string_result_t containing a the symbol as a C string
+ *  Returns a string_result_t containing the symbol as a C string
  */
 string_result_t string_get_at(const string_t *str, size_t position) {
     string_result_t result = {0};
@@ -418,17 +418,18 @@ string_result_t string_get_at(const string_t *str, size_t position) {
     }
 
     int char_len = utf8_char_len((unsigned char)*ptr);
-    char *symbol = malloc(char_len + 1);
-    if (symbol == NULL) {
+    char *utf8_char = malloc(char_len + 1);
+    if (utf8_char == NULL) {
         result.status = STRING_ERR_ALLOCATE;
         SET_MSG(result, "Cannot allocate memory");
 
         return result;
     }
 
-    memcpy(symbol, ptr, char_len);
-    symbol[char_len] = '\0';
+    memcpy(utf8_char, ptr, char_len);
+    utf8_char[char_len] = '\0';
 
+    result.value.symbol = utf8_char;
     result.status = STRING_OK;
     SET_MSG(result, "Symbol successfully retrieved");
 

src/string.h

@@ -27,7 +27,7 @@ typedef struct {
     uint8_t message[RESULT_MSG_SIZE];
     union {
         string_t *string; // For new, reverse, trim
-        char *c_str; // For get_at
+        char *symbol; // For get_at
         int64_t idx; // For substring search
         bool is_equ; // For comparison
         struct { // For split

usage.c

@@ -25,10 +25,12 @@
 #include "src/vector.h"
 #include "src/map.h"
 #include "src/bigint.h"
+#include "src/string.h"
 
 static int vector_usage(void);
 static int map_usage(void);
 static int bigint_usage(void);
+static int string_usage(void);
 
 static vector_order_t cmp_int_asc(const void *x, const void *y);
 static vector_order_t cmp_int_desc(const void *x, const void *y);
@@ -52,6 +54,11 @@ int main(void) {
     st = bigint_usage();
     if (st) { return st; }
 
+    SEP(50);
+
+    st = string_usage();
+    if (st) { return st; }
+
     return 0;
 }
 
@@ -524,3 +531,94 @@ int bigint_usage(void) {
 
     return 0;
 }
+
+int string_usage(void) {
+    // Create a new string
+    string_result_t res = string_new("Hello, ");
+    if (res.status != STRING_OK) {
+        printf("Error: %s\n", res.message);
+
+        return 1;
+    }
+
+    string_t *str1 = res.value.string;
+    printf("Created string: \"%s\"\n", str1->data);
+    printf("Character count: %zu (%zu actual bytes)\n\n", string_len(str1), str1->byte_size);
+
+    // Concatenation of strings
+    string_result_t res_suffix = string_new("World! 🦜");
+    if (res_suffix.status != STRING_OK) {
+        printf("Error: %s\n", res.message);
+
+        return 1;
+    }
+
+    string_t *suffix = res_suffix.value.string;
+    printf("Created another string: \"%s\"\n", suffix->data);
+    printf("Character count: %zu (%zu actual bytes)\n\n", string_len(suffix), suffix->byte_size);
+
+    string_result_t res_cat = string_concat(str1, suffix);
+    if (res_cat.status != STRING_OK) {
+        printf("Error: %s\n", res_cat.message);
+
+        return 1;
+    }
+    string_destroy(suffix);
+   
+    string_t *concat_str = res_cat.value.string;
+    printf("Concatenation result: \"%s\"\n\n", concat_str->data);
+
+    // Uppercase string
+    string_result_t res_upper = string_to_upper(concat_str);
+    if (res_upper.status != STRING_OK) {
+        printf("Error: %s\n", res_upper.message);
+
+        return 1;
+    }
+    printf("Uppercase: \"%s\"\n", res_upper.value.string->data);
+    string_destroy(res_upper.value.string);
+
+    // Lowercase string
+    string_result_t res_lower = string_to_lower(concat_str);
+    if (res_lower.status != STRING_OK) {
+        printf("Error: %s\n", res_lower.message);
+
+        return 1;
+    }
+    printf("Lowercase: \"%s\"\n\n", res_lower.value.string->data);
+    string_destroy(res_lower.value.string);
+
+    // Reverse string
+    string_result_t res_rev = string_reverse(concat_str);
+    if (res_rev.status != STRING_OK) {
+        printf("Error: %s\n", res_rev.message);
+
+        return 1;
+    }
+    printf("Reversed: \"%s\"\n\n", res_rev.value.string->data);
+    string_destroy(res_rev.value.string);
+
+    // Change first character of the string
+    string_result_t res_set = string_set_at(concat_str, 0, "J");
+    if (res_set.status != STRING_OK) {
+        printf("Error: %s\n", res_set.message);
+
+        return 1;
+    }
+    printf("Updated string: \"%s\"\n\n", concat_str->data);
+
+    // Get character from string (the emoji)
+    string_result_t res_get = string_get_at(concat_str, 14);
+    if (res_get.status != STRING_OK) {
+        printf("Error: %s\n", res_get.message);
+
+        return 1;
+    }
+    printf("Extracted symbol: \"%s\"\n", res_get.value.symbol);
+    free(res_get.value.symbol);
+
+    string_destroy(concat_str);
+    string_destroy(str1);
+
+    return 0;
+}