c remove the first character of an array

Question

I have a string:

str1 = "abcabcabc";

How can I remove the first character? I would like the end result to be:

str1 = "bcabcabc";

Answer 1

If you have a character pointer to a string like:

char *s = "This is my string";

then you can just do s++.

If you have a character array, your best bet may be to have a pointer to that array as well:

char s[] = "This is my string";
char *ps = s;

then you can do ps++ and make sure you use ps rather than s.

If you don't want to have a separate pointer to your array then you can use memmove to copy the data:

memmove (s, s+1, strlen (s+1) + 1); // or just strlen (s)

though none of those will work for an initially empty string so you'll have to check that first. Also keep in mind it's not advisable to attempt modifying string literals in this way (or any way, really) since it's undefined as to whether that's allowed.

Another solution is to simply code up a loop:

for (char *ps = s; *ps != '\0'; ps++)
    *ps = *(ps+1);
*ps = '\0';

This will work for all strings, empty or otherwise.

Answer 2

Pointer tricks (zero-cost):

char* s = "abcd";
char* substr = s + 1;
// substr == "bcd"

Or:

char s[] = "abcd";
char* substr = s + 1;
// substr == "bcd"

---

In-place via memmove:

char s[] = "abcd";
char* substr = s + 1;
memmove(s, substr, strlen(substr) + 1);
// s == "bcd"

Notice that we must use char[] rather than char*, which would refer to read-only memory, as described here. Furthermore, one should not use strcpy in-place because the src and dest must not overlap for strcpy.

---

Into a new string via strcpy:

char* src = "abcd";
char* substr = src + 1;
char dest[strlen(substr) + 1];
strcpy(dest, substr);
// dest == "bcd"

---

Into a new string via C++'s std::string::substr:

std::string src = "abcd";
std::string dest = src.substr(1);
// dest == "bcd"

---

Into a new string via C++'s std::copy:

std::string src = "abcd";
std::string dest;
std::copy(src.begin() + 1, src.end(), std::back_inserter(dest));
// dest == "bcd"

---

There's a couple dozen other ways (particularly when including C++), but I'll stop here. :)

Answer 3

If you really meant to say

char str1 [] = "abcabcabc";

Then the easiest thing is

str1 = &str1[1];

If you want to modify the actual data, then you have to just move everything up one position. You can use a loop for that or memmove(). A recursive function is overkill.

If you really meant C++ and you're using the string object then you can use

str1 = str1.substr(1);

Answer 4

Here is one way to do it:

int index = 0; //index to cull
memmove( &word[ index ] , &word[ index +1], strlen( word ) - index) ;

Answer 5

Well as far as i know if you are worried about memory allocation you have to copy (str1+1) into a new string that you personally allocate memory for, then free the first pointer. The really simple way to do it would be to just increment str1 with str1++; That would make it point one character farther than it used to and give you the desired result with just a line of code.

Answer 6

#include <stdio.h>
#include <conio.h>
main(){
   char a[10];
   int i;
   gets(a);

   for (i = 0; a[i] != '\0'; i++) {
      a[i] = a[i + 1];
   }

   printf("\n");
   puts(a);
   getch();
}