Since c is holding the address of an integer pointer, its type should be int**: int **c; c = &a; The entire program becomes: #include <stdio.h> int main(){ int b=10; int *a; a=&b; int **c; c=&a; printf(“%d”,(**c)); //successfully prints 10 return 0; }
Going to sleep until the scheduler wakes you is the normal/prefered thing to do. Spinning (the alternative way to wait, without sleeping) is less usual and has the following effects: Keeps the CPU busy, and prevents other threads from using the CPU (until/unless the spinning thread finishes its timeslice and is prempted) Can stop spinning … Read more
From LSP (page 28): Yes, this function’s name is missing an e. Ken Thompson, the creator of Unix, once joked that the missing letter was his largest regret in the design of Unix.
When the main thread returns (i.e., you return from the main function), it terminates the entire process. This includes all other threads. The same thing happens when you call exit. You can avoid this by calling pthread_exit. The purpose of pthread_detach is to make it so you don’t need to join with other threads in … Read more
The x86-64 System V ABi doc may help. It’s a reference, albeit lightweight. The Variable Argument List reference starts on page 54, then it goes on, page 56-57 documents va_list: The va_list Type The va_list type is an array containing a single element of one structure containing the necessary information to implement the va_arg macro. … Read more
A conforming standard library file math.h is not only not required to, but actually must not define M_PI by default. In this context ‘by default’ means that M_PI must only get defined through compiler-specific tricks, most often undefined behavior through the use of reserved identifiers. Just define the constant yourself (you can use the name … Read more
No, but you can create small minimum scopes to achieve this since all scope local variables are destroyed when the scope is exit. Something like this: void foo() { // some codes // … { // create an extra minimum scope where a is needed int a; } // a doesn’t exist here }
I’m not sure how the manual can be any clearer! fork() creates a new process, so you now have two identical processes. To distinguish between them, the return value of fork() differs. In the original process, you get the PID of the child process. In the child process, you get 0. So a canonical use … Read more
Using floating point numbers, 0.0 / 0.0 isn’t a “divide by zero” error; it results in NaN. This C program prints -nan: #include <stdio.h> int main() { float x = 0.0 / 0.0; printf(“%f\n”, x); return 0; } In terms what NaN looks like to the computer, two “invalid” numbers are reserved for “signaling” and … Read more
No, Standard C does not support either. Why do you feel you need to convert your C++ code to C? That could get quite tricky – I’d have thought writing wrappers would be the way to go, if your C++ must be callable from C.