volatile tells the compiler not to optimize anything that has to do with the volatile variable. There are at least three common reasons to use it, all involving situations where the value of the variable can change without action from the visible code: When you interface with hardware that changes the value itself; when there’s … Read more
Executive summary: No. i++ could potentially be slower than ++i, since the old value of i might need to be saved for later use, but in practice all modern compilers will optimize this away. We can demonstrate this by looking at the code for this function, both with ++i and i++. $ cat i++.c extern … Read more
Archive libraries (.a) are statically linked i.e when you compile your program with -c option in gcc. So, if there’s any change in library, you need to compile and build your code again. The advantage of .so (shared object) over .a library is that they are linked during the runtime i.e. after creation of your … Read more
From the C99 Standard (the emphasis is mine) 6.5.3.4/2 The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand. The result is an integer. If the type of the operand is a … Read more
Yes. In fact Axel Schreiner provides his book “Object-oriented Programming in ANSI-C” for free which covers the subject quite thoroughly.
Look up the access() function, found in unistd.h. You can replace your function with if (access(fname, F_OK) == 0) { // file exists } else { // file doesn’t exist } Under Windows (VC) unistd.h does not exist. To make it work it is necessary to define: #ifdef WIN32 #include <io.h> #define F_OK 0 #define … Read more
Hacky but works for me: #define BYTE_TO_BINARY_PATTERN “%c%c%c%c%c%c%c%c” #define BYTE_TO_BINARY(byte) \ (byte & 0x80 ? ‘1’ : ‘0’), \ (byte & 0x40 ? ‘1’ : ‘0’), \ (byte & 0x20 ? ‘1’ : ‘0’), \ (byte & 0x10 ? ‘1’ : ‘0’), \ (byte & 0x08 ? ‘1’ : ‘0’), \ (byte & 0x04 ? … Read more
“%f” is the (or at least one) correct format for a double. There is no format for a float, because if you attempt to pass a float to printf, it’ll be promoted to double before printf receives it1. “%lf” is also acceptable under the current standard — the l is specified as having no effect … Read more
The difference here is that char *s = “Hello world”; will place “Hello world” in the read-only parts of the memory, and making s a pointer to that makes any writing operation on this memory illegal. While doing: char s[] = “Hello world”; puts the literal string in read-only memory and copies the string to … Read more
In (ANSI) C99, you can use a designated initializer to initialize a structure: MY_TYPE a = { .flag = true, .value = 123, .stuff = 0.456 }; Other members are initialized as zero: “Omitted field members are implicitly initialized the same as objects that have static storage duration.” (https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html)