当我尝试实现一个反转数组的函数时，为什么输入数组和输出数组都损坏了？

Question

I'm Programming in C, using Linux GCC Compiler. I'm very much new to programming.

I'm confused as to why my in[] char array would be changed at all in the function. Doesn't the code simply count the amount of subscripts in in[] and then copy its contents into out[] but backwards? How is it being changed in the function?

/*reverse in to out*/
void reverse(char in[], char out[]) {
    int i, l,b;
    b = i = l = 0;

    while (in[i] != '\0')
        ++i;

    for(l=i;l > 0; l--) {
        in[l] = out[b];
        ++b;
   }
   return;
}

Answer 1

Your assignment statement is backwards.

in[l] = out[b];

Means "Assign the value in array out at index b to array in index l ". This line should instead be

out[b] = in[l];

And BTW, you don't need an empty return statement, you can simply omit this in a void function.

Answer 2

for(l=i-1;l >= 0; l--) {
    out[b] = in[l];
    ++b;
}
out[b] = '\0';

Four problems fixed: start at i-1 , test for l>=0 , reverse the assignment, and terminate out with a null character.

Also, a good idea is to use const when a function argument will not be changed. In this case, const char in[] would let you spot the assignment error because the compiler would give you a compile time error.

Answer 3

You can use strlen :

for(l=strlen(in), b=0; l>=0; l--)
    out[b++] = in[l];

// ensure null terminated so strlen out works
out[b] = '\0';

This assumes out is wide enough for in AND in is null terminated