![]() ![]() What happens if you’ve been too cheap when allocating the string and the actual content is longer than expected. No, I’m not worried about the memory overhead, but I’m seriously concerned about buffer overflows. ![]() Moreover, this is a local variable, so we’ll reclaim the memory as soon as it gets out of scope. You’re right, there can be up to 14 unused bytes in the array, but this is nothing compared to what you loose from the heap management data and from the heap fragmentation. You probably worry about the overhead caused by the unused bytes in the array. Now you can see a major difference between the two approaches: the Arduino version uses a String, which allocates the right number of bytes in the heap, whereas the C version allocates a fixed number of bytes in the stack. In this case, we used a simple char array large enough to store the string with the terminator. In addition to calling sprintf(), we need to allocate the sequence of characters. On Arduino you would write:Ĭhar s sprintf ( s, "%f", weight ) Īs you can see, the C version is a little more verbose. For example, suppose you have a float that contains the weight of something, and you want to display it. The major difference between printf() and Serial.print() is that, before passing the things you want to write, you must tell printf() the type of those things. printf() is the equivalent of Arduino’s Serial.print(). If you’ve done any C programming, you probably used the printf() function, which writes things to the terminal. Everything you can do with the String class, you can also do with a C string, even if it’s usually more complicated. Indeed, the String class is just a fancy wrapper on top of a C string. Keep this picture in mind because every time you write a string literal, this is exactly what goes in memory, whether you use the String class or not. The picture below shows how the bytes of the string “hello” are laid out in RAM. We call this last byte the “terminator” because it marks the end of the sequence. In C, a string is a contiguous sequence of characters ended by a 0. As you probably know, we can use any C feature in C++, and that what we’re going to do in this article: we’ll formats strings as C programmers do.įirst, let’s look at how the C language models strings. So how can we get rid of the String class? We’ll take some distance with C++ for a moment and get back to plain old C. Use several String instances in your program, and soon, the RAM is full of holes like Swiss cheese. The problem with the String class is that it forces you to use the heap and allocates blocks of variables size. To prevent fragmentation, you should always allocate blocks of the same size, or better, don’t use the heap at all. String url = String ( "" ) + user + "/repos?page=" + page What’s the problem with the String class?īut why should we avoid the String class? As I explained in a previous article, heap fragmentation is a major concern in embedded programming. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |