Question

I wrote following 2 ltrim functions (function which removes white-spaces from left side of the string):

1. (putting here this code to not get such code as an answer)

void ltrim(char * str, int size)
{
    char const *start = str;
    char const *end = start + size;
    for(;*start && (*start==' ' || *start=='\n' || *start=='\r' || *start=='\t');++start);

    while(start != end)
    {
        *str = *start;
        ++start;
        ++str;
    }
    *str='\0';
}

2.

void ltrim(char * str, int size)
{
    char const *start = str;
    char const *end = start + size;
    for(;*start && (*start==' ' || *start=='\n' || *start=='\r' || *start=='\t');++start);
    memcpy(str, start, end-start);
    *(str + (end - start)) = '\0';
}

Does second version safe?

P.S. I have tried and it works, but not sure that memcpy is safe in this case.

Answer 1

When source and destination overlap you should use memmove rather than memcpy.

From the memcpy man page:

The memcpy() function copies n bytes from memory area src to memory area dest. The memory areas should not overlap. Use memmove(3) if the memory areas do overlap.