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clvaluememset

lvalue required on incrementing a void pointer even after proper casting

I am implementing memset() method. Below is the code snippet:

void my_memset(void* ptr, int n, size_t size)
{
    unsigned int i;

    for( i = 0; i < size; ++i, ++(char*)ptr )
            *(char*)ptr = n;
}

I am getting the error as: 

prog.cpp: In function ‘void my_memset(void*, int, size_t)’:
prog.cpp:8: error: lvalue required as increment operand

When i change the type of ptr from void* to int*, it compiles successfully.

Why it is asking for lvalue?

Solution 
  • void my_memset(void* ptr, int n, size_t size)
{
    char *cptr = (char *)ptr;
    char *limit = cptr + size;

    for(; cptr < limit; cptr++) {
        *cptr = n;
    }
}

    you can't increment through a cast like that, and you shouldn't want to.