Substr

Is there no equivalent to the substr function in c++ in c???

You can use the sprintf function to simulate that.

I think he means strstr(), which finds a string within a string.

To extract a substring from a string, use strncpy, as in
strncpy( dest, &src[start], len );
dest[len] = '\0';

I took hk's reply in this manner:

Code:

---

#include <stdio.h>

char *substr(char *dst, const char *src, int start, int len)
{
  sprintf(dst, "%.*s", len, &src[start]);
  return dst;
}

int main(void)
{
  const char src[] = "Here is some text.";
  char dst[sizeof src];
  printf("dst = \"%s\"\n", substr(dst,src,5,7));
  return 0;
}

/* my output
dst = "is some"
*/

---

There's no substr function in the C standard libraries. The standard libraries don't like using dynamic memory with strdup as the only exception I can think of. C++ has a bunch though, I don't know why but I suspect it's because they don't want to give people the burden of having to free memory themselves.

I wrote a substr function once which was supposed to be like the Perl substr but there were some limitations since I couldn't replace text on a string of unknown size so I had the function make a copy instead and that 0 and NULL is used to signal unused parameters.

Code:

---

#include <stdlib.h>

char* substr (const char* string, int pos, int len, const char* replace)
{
        char* substring;
        int  i;
        int  length;

        if (string == NULL)
                return NULL;
        length = strlen(string);
        if (pos < 0) {
                pos = length + pos;
                if (pos < 0) pos = 0;
        }
        else if (pos > length) pos = length;
        if (len <= 0) {
                len = length - pos + len;
                if (len < 0) len = length - pos;
        }
        if (pos + len > length) len = length - pos;
        if (replace != NULL) {
                if ((substring = malloc(sizeof(*substring)*(length-len+strlen(replace)+1))) == NULL)
                        return NULL;
                for (i = 0; i != pos; i++) substring[i] = string[i];
                pos = pos + len;
                for (len = 0; replace[len]; i++, len++) substring[i] = replace[len];
                for (; string[pos]; pos++, i++) substring[i] = string[pos];
                substring[i] = '\0';
        }
        else {
                if ((substring = malloc(sizeof(*substring)*(len+1))) == NULL)
                        return NULL;
                len += pos;
                for (i = 0; pos != len; i++, pos++)
                        substring[i] = string[pos];
                substring[i] = '\0';
        }

        return substring;
}

---

substr("some string", 5, 0, NULL)
returns "string"

substr("some string", -5, 3, NULL)
returns "str"

substr("some string", 4, 0, "thing")
returns "something"

free() needs to be called on the string returned after it's use.