fix: fix free hex_str

ChaCha20_DRBG.c

@@ -764,8 +764,8 @@ int main() {
   // char *filename; filename 未分配内存
   char filename[100]; // 假设文件名长度不超过 99 个字符
   printf("Enter the name of the saved file: ");
-  // scanf("%s", filename);
-  strcpy(filename, "1.txt");
+  scanf("%s", filename);
+  // strcpy(filename, "1.txt");
 
   // 生成的比特串保存在文本文件中
   FILE *file = fopen(filename, "w");
@@ -775,7 +775,8 @@ int main() {
   }
 
   clock_t start_time = clock();
-
+  char *hex_str =
+      (char *)malloc(sizeof(char) * (returned_bits_len / 8 * 2 + 1));
   for (int j = 1; j <= returned_bits_num; ++j) {
     do {
       int zero_count = 0;
@@ -809,15 +810,14 @@ int main() {
     } while (!pass);
 
     // 将二进制数据转为十六进制后写入文件
-    char *hex_str =
-        (char *)malloc(sizeof(char) * (returned_bits_len / 8 * 2 + 1));
+    
     for (int i = 0; i < returned_bits_len / 8; ++i) {
       sprintf(&hex_str[i * 2], "%02x", returned_bits[i]);
     }
     hex_str[returned_bits_len / 8 * 2] = '\0';
     fprintf(file, "%s\n", hex_str); // 写入带有换行符的十六进制字符串
-    free(hex_str);
   }
+  free(hex_str);
 
   clock_t end_time = clock();
   double execution_time = (double)(end_time - start_time) / CLOCKS_PER_SEC;