strcpy和数组的异常行为

Question

I am writing a simple string substitution function and I have a quite interesting error. Shouldn't strcpy just overwrite the buf\\streamBuf value? How come it concatenates arrays?

int main()
{
    char buf[512];
    strcpy(buf, "Test\nInput\nHere\n");

    char fromCh[2] = "\n";
    char toCh[4] = "\\n ";
    stripChars(buf, fromCh, toCh);
    printf("Here's your buf: %s", buf);
    return 0;
}

void stripChars(char *streamBuf, char* fromCh, char *toCh){
        char strTemp[512];
        int i=0;
        int iLenFrom = strlen (fromCh);
        int iLenTo = strlen (toCh);
        while (*streamBuf)
        {
            if (strncmp (streamBuf, fromCh, iLenFrom) == 0)
            {
                strncpy (&(strTemp[i]), toCh, iLenTo);
                i += iLenTo;
                streamBuf += iLenFrom;
            }
            else
            {
                strTemp[i++] = *streamBuf;
                streamBuf++;
            }
        }
    strTemp[i] = '\0';
    strcpy(streamBuf, strTemp);

    printf("Here's your strTemp: %s \n", strTemp);
    printf("Here's your streamBuf: %s \n", streamBuf);
}

and here's my output

Here's your strTemp: Test\n Input\n Here\n  
Here's your streamBuf: Test\n Input\n Here\n  
Here's your buf: Test
Input
Here
Test\n Input\n Here\n 
Process finished with exit code 0

Answer 1

Here

streamBuf += iLenFrom;

and here

streamBuf++;

you change streamBuf

Consequently it will no longer be equal to buf in main .

So changes to data pointed to by streamBuf is no longer the same as changing data pointed to by buf

If you want to see what happens, you can add prints of the pointer values, like:

printf("buf is at %p\n", (void*)buf);
stripChars(buf, fromCh, toCh);

and

void stripChars(char *streamBuf, char* fromCh, char *toCh){
    printf("streamBuf is at %p\n", (void*)streamBuf);
    ....
    ....
    printf("streamBuf is at %p\n", (void*)streamBuf);
    printf("Here's your streamBuf: %s \n", streamBuf);
}

Answer 2

How come it concatenates arrays?

That's because you are changing where streamBuf points to in the function.

Keep track of the original location of where streamBuf points to and use it at the end of the function.

void stripChars(char *streamBuf, char* fromCh, char *toCh)
{
   char* originalPointer = streamBuf;

   ...

   streamBuf = originalPointer;
   strcpy(streamBuf, strTemp);

   printf("Here's your strTemp: %s \n", strTemp);
   printf("Here's your streamBuf: %s \n", streamBuf);
}