Cut out section of string

Question

I wouldn't mind writing my own function to do this but I was wondering if there existed one in the string.h or if there was a standard way to do this.

char *string = "This is a string";

strcut(string, 4, 7);

printf("%s", string); // 'This a string'

Thanks!

Answer 1

If you are doing this in C and know the offset then it's pretty simple.

char string[] = "my string";
char *substring;
substring = &string[2];

printf("%s", substring);

EDIT: If you wanted to shift the string.

char string[] = "my string";

int i = 0;
int offset = 2;

for( i = 0; string[i+offset] != '\0'; i++ ) {
 string[i] = string[i + offset];
}
string[i] = '\0';

Answer 2

If you're talking about getting rid of the middle of the string and moving the rest earlier in place, then I don't think there's a standard library function for it.

The best approach would be to find the end of the string, and then do an O(cut_size) cycle of shifting all the characters to the new location. In fact, there's a similar common interview question.

You have to be careful about using things like memory copy since the destination buffer overlaps with the source.

Answer 3

Use memmove to move the tail, then put '\0' at the new end position. Be careful not to use memcpy - its behaviour is undefined in this situation since source and destination usually overlap.

Answer 4

You can just tell printf to cut the interesting parts out for you:

char *string = "This is a string";
printf("%.*s%s", 4, string, &string[7]); // 'This a string'

:-)

Answer 5

You may be able to accomplish what you want and avoid writing a new function with a combination of strncpy and strcat:

#include <stdio.h>
#include <string.h>
int main(void)
{
  char   newStr[10];
  char   origStr[] = "This is a string";
  strncpy(newStr, origStr, 4);
  strcat(newStr, &origStr[7]);
  printf("newStr = %s\n", newStr);
  return(0);
}

For me, this outputs "This a string" (quotes mine), using Borland's free command line compiler on Windows XP. You can check out string.h at: http://opengroup.org/onlinepubs/007908799/xsh/string.h.html