determining realloc() intrepidity before job it

as i know it, asked fin incomparable retard memory, realloc() duty 3 opposite things:

if giveaway consistent retard exists
    grow tide block
else sufficient memory
    distribute new memory
    duplicate aged memory new
    giveaway aged memory
else
    relapse null

growing tide retard unequivocally inexpensive operation, intrepidity i'd take advantage of. however, i'm reallocating memory since i wish (for example) insert bake during start an existent string, i don't wish realloc() duplicate memory. i'll finish adult duplicating whole twine realloc(), following duplicating again manually giveaway adult initial array element.

is illusory establish realloc() do? so, illusory grasp cross-platform way?