CareerCup

Total Six bug in the code

1. No validation of the inputs, if NULL is passed to any of the input function will crash while dereferencing (while(*s1)).
2. Buffer is not allocated based on the sum of the length of the input string, which will lead to buffer overrun (in this case stack overrun) if the combined string length is greater than 1024 (char buffer[1024]).
3. Address of the local variable is returned, buffer should be allocated on heap (dynamic memory) and its pointer should be returned (return buffer).
4. ++i is creating a byte between the two string used for concatenation to contain garbage value (buffer[++i]=s2).
5. pointer is being assigned to char value (buffer[++i]=s2).
6. The combined string is not null terminated.

2 mistakes.
1) There is a gap in between two strings (have some garbage value).
2) string not ended with '\0'.

buffer array is local to the function. It should be declared static.

4) No check on length , if length of (S1+S2) > 1024 , we are writing beyond the boundary of array.

BTW, any idea how long MS takes to declare results for written tests ?

1) There is a gap in between two strings (have some garbage value).
2) string not ended with '\0'.
3) size of buffer not enough, if size of (S1+S2) > 1024.
4) In copying second string [ buffer[++i]=s2; ] RHS should be *s2.

we are not allocating the space via malloc so it shd be an error .... wat does gap betw strings mean ???

1> return pointer to stack memory
2> size not checked
3> we were doing i++ then we switched to ++i so there is has been a double increment
4> and no null assigned at end

/* find the bug in the following code which concatenates 2 strings ---*/
char * concatenate(char *s1,char *s2) 
{
    /* 1) s1 and s2 can be null and the method never checks if they are initialized */
    char buffer[1024];   /* 2) can produce overflow because lenghts of s1 and s2 are unknown */
    int i=0;
    while(*s1)
    {
        buffer[i++]=*s1;
        s1++;
    }
    while(*s2)
    {
        buffer[++i]=s2;  /* 3) ++i jumps an additional character */ /* 4) can't pass char* to char */
        s2++; 
    }
    return buffer;    /* 5) buffer doesn't end with null character */ 
/* 6) can't return a pointer to a previous declared function, must use malloc, not static */
}

dont u all think that the two strings are having ther original pointers ass1 and s2... now if we perform s1++,we are changing s2,which means that access to array is lost from begining,hence..it will give compiler error..i.e."lvalue required in function main"