Getting string between two given characters

Question

quote I have input something like !Hello world! - 123 123 - and I need to get it into struct { char *string; int a; int b;} Can you help me?

typedef struct {
    int a;
    int b;
    char *string;
} Smth;
//-----------(size=(already known size of input))
Smth *smth = (*Smth)malloc(sizeof(smth));
smth.string = (char*)malloc(sizeof(char) * size);
sscanf(input, "!%[^!]! - %d %d - ", smth.string, &smth.a, &smth.b); // doesn't work for me

Perhaps look at the rexex library like this question https://stackoverflow.com/q/64412234/1216776 — stark, Jan 03 '21 at 14:08
It would help if you show us how `smth` is declared and "allocated"? — Bo R, Jan 03 '21 at 14:31

bruno · Answer 1 · 2021-01-03T14:32:12.167

before you edit your question

the call

sscanf("!%[^!]! - %d %d - ",string,&a,&b);

is not the one you want, you missed to give the string to parse as the first argument, so the string to parse is the format you wanted to use and the used format is the perhaps not initialized value of string

You wanted :

#include <stdio.h>

int main()
{
  char string[32];
  int a,b;
  const char * i = "!Hello world! - 123 123 -";
  
  if (sscanf(i, "!%31[^!]! - %d %d - ", string,&a,&b) == 3)
    printf("'%s' %d %d\n", string, a, b);
  else
    put("error");
  
  return 0;
}

does the work :

pi@raspberrypi:/tmp $ gcc -Wall f.c
pi@raspberrypi:/tmp $ ./a.out
'Hello world' 123 123
pi@raspberrypi:/tmp $

Notice I added in your original format a max length for the read string to not take the risk to write out of string and then to have an undefined behavior. If you do not want to manage yourself the array for string you can use the option %m but is not always available.

Bo R · Answer 2 · 2021-01-03T14:42:47.313

2

You are lacking the input string for sscanf. See example below.

#include <stdio.h>
#include <stdlib.h>

typedef struct
{
   int a;
   int b;
   char *string;
} Smth;


int main(void)
{
   Smth smth;
   sscanf(
      "!Hello world! - 123 123 -",
      "!%m[^!]! - %i %i -",
      &smth.string,
      &smth.a,
      &smth.b);
   printf("Str: `%s' a:%d b:%d\n", smth.string, smth.a, smth.b);
   free(smth.string);
   return 0;
}

UPDATE: Given your change in question

#include <stdio.h>
#include <stdlib.h>

typedef struct
{
   int a;
   int b;
   char* string;
} Smth;


int main(void)
{
   size_t size  = 30u;
   char input[] = "!Hello world! - 123 123 -";

   Smth* smth   = (Smth*) malloc(sizeof(Smth));
   smth->string = (char*) malloc(sizeof(char) * size);
   sscanf(input, "!%29[^!]! - %d %d - ", smth->string, &smth->a, &smth->b);

   printf("Str: %s a:%d b:%d\n", smth->string, smth->a, smth->b);

   free(smth->string);
   free(smth);

   return 0;
}

edited Jan 03 '21 at 14:42

answered Jan 03 '21 at 14:20

Bo R

2,334
1
9
17

@DanielBlažek I see a `char * string` in your struct. Did you allocate memory for that string? You need memory to contain the string and `sscanf()` won't do that for you. – Blastfurnace Jan 03 '21 at 14:26
@Blastfurnace the format uses the option *m*, I also speak about that way in my answer – bruno Jan 03 '21 at 14:29
@bruno Oh, it's the first time I've seen that GNU lib C extension. – Blastfurnace Jan 03 '21 at 14:32
@Blastfurnace yes, this is practical but not standard – bruno Jan 03 '21 at 14:33
@bruno It's also in POSIX. Hmm, I learn something new every day. – Blastfurnace Jan 03 '21 at 14:34
@Blastfurnace yes, even 'only' answering we learn ;-) – bruno Jan 03 '21 at 14:41

Getting string between two given characters

2 Answers2