Re-posting a modified version of my answer from optimized sum of an array of doubles in C, since that question got voted down to -5. The OP of the other question phrased it more as “what else is possible”, so I took him at his word and info-dumped about vectorizing and tuning for current CPU … Read more
No, you can’t. The compiler doesn’t know what the pointer is pointing to. There are tricks, like ending the array with a known out-of-band value and then counting the size up until that value, but that’s not using sizeof(). Another trick is the one mentioned by Zan, which is to stash the size somewhere. For … Read more
It needs to change the variable. Since all arguments in C are passed by value you need to pass a pointer if you want a function to be able to change a parameter. Here’s a super-simple example showing it: void nochange(int var) { // Here, var is a copy of the original number. &var != … Read more
Any modern operating system will clean up everything after a process terminates, but it’s generally not a good practice to rely on this. It depends on the program you are writing. If it’s just a command line tool that runs and terminates quickly, you may not bother cleaning up. But be aware that it is … Read more
The only places you can omit brackets are for the bodies of if-else, for, while, or do-while statements if the body consists of a single statement: if (cond) do_something(); for (;;) do_something(); while(condition) do_something(); do do_something(); while(condition); However, note that each of the above examples counts as single statement according to the grammar; that means … Read more
Since the size of the array you declare is not constant, what you have is an Variable Length Array(VLA). VLA are allowed by the c99 standard but there are some limitations associated with it. You cannot have an variable length array with static or extern storage class specifier. You have an VLA with static storage … Read more
I’d suggest writing your own function to do the piping/forking/system-ing for you. You could have the function spawn a process and return read/write file descriptors, as in… typedef void pfunc_t (int rfd, int wfd); pid_t pcreate(int fds[2], pfunc_t pfunc) { /* Spawn a process from pfunc, returning it’s pid. The fds array passed will * … Read more
I like the idea of using freopen. You might also be able to redirect stdout to a pipe using dup and dup2, and then use read to grab data from the pipe. Something like so: #include <stdio.h> #include <stdlib.h> #include <unistd.h> #define MAX_LEN 40 int main( int argc, char *argv[] ) { char buffer[MAX_LEN+1] = … Read more
You could try a combination of strptime and mktime struct tm tm; time_t epoch; if ( strptime(timestamp, “%Y-%m-%d %H:%M:%S”, &tm) != NULL ) epoch = mktime(&tm); else // badness
sizeof is always computed at compile time in C89. Since C99 and variable length arrays, it is computed at run time when a variable length array is part of the expression in the sizeof operand. Same for the evaluation of the sizeof operand: it is not evaluated in C89 but in C99 if the operand … Read more