Deleting substring in a string with delimiters in C [closed] - c

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I need a help with a program (without using strtok() function) that should be doing this:
If the input is
car;dog;pet;elephant
and if the argument is 2, the ouput should be:
car;pet;elephant
if the argument is 4, the output should be:
car;dog;pet
and so on.
I've tried a lot of different solutions but nothing seems to work. So if anybody could help me, I would be really glad.
Thank you.

Answer 1

I think this solution always works with valid input.
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
if (argc != 3)
return 1;
int x = atoi(argv[2]);
char *s = argv[1], *d = argv[1];
while (*s)
{
if (x == 0)
{
--x;
while (*s && *s != ';')
++s;
if (*s)
++s;
else
break;
}
if (*s == ';')
--x;
*d++ = *s++;
}
if (*(d - 1) == ';')
*(d - 1) = '\0';
else
*d = '\0';
puts(argv[1]);
return 0;
}

Answer 2

Here is a function to construct a new csv line with the field number pos (1-based) removed:
#include <stdlib.h>
#include <string.h>
char *removeField(const char *str, char delim, int pos)
{
char *out;
const char *p, *q;
size_t len1, len2;
int i, nsep = 0;
if (str == NULL)
return NULL;
/* skip the fields before the target field */
for (p = str, i = 1; *p && i < pos; i++) {
while (*p && *p != delim)
p++;
if (*p == delim) {
p++;
nsep++;
}
}
/* skip the field to remove */
for (q = p; *q && *q != delim; q++)
continue;
if (*q == delim) {
/* if there are more fields, skip the delimiter */
q++;
} else {
/* otherwise remove the trailing delimiter if the removed field was
the last one but not the first one */
if (pos > 1 && nsep == pos - 1)
p--;
}
/* allocate the exact amount of bytes */
len1 = p - str;
len2 = strlen(q);
out = malloc(len1 + len2 + 1);
if (out != NULL) {
/* copy the left and right parts */
memcpy(out, str, len1);
memcpy(out + len1, q, len2 + 1);
}
/* return the new CSV line or NULL if allocation failure */
return out;
}

Answer 3

Here is the function removing the substring from the "csv style" line. It takes info the account empty strings and (probably most as I did not properly test it) border cases.
It is not using "heavy" string functions like strtok or strdup as I believe this exercise is to write it using arrays or pointers.
char *dupAndDelete(const char *str, char delim, int pos)
{
char *out = NULL;
int cpos = 1;
if(str)
{
out = malloc(strlen(str) + 1);
char *wrk = out;
if(out)
{
while(*str)
{
if(cpos == pos)
{
while(*str && *str != delim)
str++;
}
else
{
*wrk++ = *str;
}
if(*str == delim)
{cpos++;}
if(*str) str++;
}
if(wrk > out)
if(*(wrk - 1) == delim && cpos == pos)
wrk--;
*wrk = 0;
}
}
return out;
}
int main(void)
{
char *str = ";;car;;dog;pet;elephant;;";
char *output;
for(int pos = 0; pos < 12; pos++)
{
output = dupAndDelete(str, ';', pos);
if(output) printf("pos = %2d str = \"%s\"\n", pos, output);
fflush(stdout);
free(output);
}
return 0;
}

Answer 4

You can search a ; with strchr()
This code searches the index you want to remove (1-based indexes)
int main(void)
{
for (size_t i = 0; i < 6; i++)
{
// This is you argument
int arg2 = i;
printf("%ld: ", i);
char *s = strdup(";car;dog;pet;elephant");
char *curr = s;
for (int i = 0; curr && i < arg2; i++)
curr = strchr(curr + 1, ';');
if (!curr)
{
printf("%s\n", s);
free(s);
continue;
}
char *next = strchr(curr + 1, ';');
if (!next)
{
*curr = 0;
}
else
{
size_t offset = next - curr;
size_t len = strlen(s);
for (size_t i = curr - s; i < len; i++)
s[i] = (i + offset < len ? s[i + offset + (curr == s)] : 0);
}
printf("%s\n", s);
free(s);
}
return 0;
}

Answer 5

Without any control/argument inspection, I think this is what you're looking for:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char ** argv) {
if (argc < 3) {
printf("Argument missing!\n");
return 1;
}
char * output = calloc(sizeof(char), strlen(argv[1]));
int cnt = 1;
int memb = atoi(argv[2]);
int outputp = 0;
char* token = strtok(argv[1], ";");
while (token != NULL) {
if (cnt != memb) {
strcat(output+outputp, token);
outputp += strlen(token);
strcat(output+outputp, ";");
outputp++;
}
token = strtok(NULL, ";");
cnt++;
}
output[outputp-1] = '\0';
printf("%s\n", output);
free(output);
return 0;
}
use:
$ ./a.out "car;dog;pet;elephant" 2
car;pet;elephant
$ ./a.out "car;dog;pet;elephant" 4
car;dog;pet
Edit: you can use strsep() instead of strtok(), then if your substring is empty, that will counts too:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char ** argv) {
if (argc < 3) {
printf("Argument missing!\n");
return 1;
}
char * output = calloc(sizeof(char), strlen(argv[1])+1);
int cnt = 1;
int memb = atoi(argv[2]);
int outputp = 0;
char * token;
while ((token = strsep(&argv[1], ";")) != NULL) {
printf("'%s'\n", token);
if (cnt != memb) {
strcat(output+outputp, token);
outputp += strlen(token);
strcat(output+outputp, ";");
outputp++;
}
cnt++;
}
output[outputp-1] = '\0';
printf("%s\n", output);
free(output);
return 0;
}