string in hex

Sometimes, I need to see characters of a string in Hex values:

void printhex(unsigned char* str)
{
    for (int j=0;j<strlen(str);j++)
        printf("%02X ", str[j] );
}

Thanks to mibrahim (encdec).

pointer to const memory

char * s = "ab";
memset(s, 0 , strlen(s)); //empy string

This code won't run because s is considered pointer to const char.
As well, this applies on a statement like this:

memcpy(s, "\0\0" , strlen(s));

That's because the compiler first reserved a memory space to hold the value "ab" then it returns to you a pointer to it. i.e. this is not considered intialization of the pointer.
Of course, defining s as an array of characters will be ok, where s will be handled as a normal variable that can be inialized not as pointer to const memory.

strlen() vs. sizeof() Tip

Only use sizeof() for locally allocated buffers.
Always use strlen() for variables passed from outside.

Why: using sizeof() with a pointer to char passed to you will return
the size of the pointer itself (which is 4 always) not the size of the
allocated space to that buffer.

Why Dynamic Allocation is slower and may fail?

Usually, memory is allocated from a large pool of unused memory area called the heap (also called the free store). Since the precise location of the allocation is not known in advance, the memory is accessed indirectly, usually via a reference. The precise algorithm used to organize the memory area and allocate and deallocate chunks is hidden behind an abstract interface and may use any of the methods described below.

Problems during fullfiling allocation request include Internal and external fragmentation.


From Wikipedia

Static vs. Dynamic vs. Automatic Variable

Static memory allocation refers to the process of allocating memory at compile-time before the associated program is executed, unlike dynamic memory allocation or automatic memory allocation where memory is allocated as required at run-time.

An application of this technique involves a program module (e.g. function or subroutine) declaring static data locally, such that these data are inaccessible in other modules unless references to it are passed as parameters or returned. A single copy of static data is retained and accessible through many calls to the function in which it is declared. Static memory allocation therefore has the advantage of modularising data within a program design in the situation where these data must be retained through the runtime of the program.

The use of static variables within a class in object oriented programming enables a single copy of such data to be shared between all the objects of that class.

Object constants known at compile-time, like string literals, are usually allocated statically. In object-oriented programming, the virtual method tables of classes are usually allocated statically.

From Wikipedia