它在处理字符串时出现分段错误？

Question

I have written the following replace function which replaces substring inside a big string as follows:

void replace(char *str1, char *str2, int start, int end)
{
    int i,j=0;
    for(i=start; i<end; i++, j++)
        *(str1+i)=*(str2+j);
}

It works fine when I put a string as replace("Move a mountain", "card", 0,4) , but when I declare a string using pointer array like char *list[1]={"Move a mountain"} and pass it to the function as replace(list[0], "card",0,4) , it gives me a segmentation fault.

Not able to figure it out. Can anybody please explain this to me?

Answer 1

The code of function replace looks fine, yet all the ways you call it introduce undefined behaviour:

First, with replace("Move a mountain", "card", 0,4) , you are passing a string literal as argument for str1 , which is modified in replace then. Modifying a string literal is undefined behaviour, and if it "works", it is just luck (more bad luck than good luck, actually).

Second char *list[1]={"Move a mountain"} is similar but introduces another issue: char*list is an array of pointers, and you initialize list[0] to point to string literal ""Move a mountain" . So passing list[0] would again lead to UB due to modifying a string literal. But then you pass list[1] , which is out of bounds and therefore introduces undefined behaviour. Again, everything can happen, segfaulting being just one such possibility.

Write

char list[] = "Move a mountain"; // copies string literal into a new and modifiable array 
replace(list, "card",0,4)

and it should work better.