Thread: assigning a string to a variable

Hi, I'm currently trying to store a string by using this notation: prvstring[STRSIZE] = str[STRSIZE]. For some reason it doesn't work. Is there a way to assign a variable equal to a string? Thank you very much!

Code:

#include<stdio.h>
#include<string.h>

int main(void)
{
#define STRSIZE 20
FILE *pf;
char str[STRSIZE]; /*Maximum size of a string is 20*/
char ustring[STRSIZE];
char *chpoint;
char prvstring[STRSIZE];

pf = fopen("input.txt","r");

if (!pf)
{
printf("Can't open the file\n");
return 0;
}

printf("Enter a string. ");
chpoint = strchr(ustring, '\n'); /*searches for "\n", address is returned if found; otherwise NULL is returned*/

if (chpoint != NULL)
{
*chpoint = 0; /*removes the \n*/
}

while (fscanf(pf, "%s",str) == 1) /*continue to scan and print strings until the EOF*/
{
int v = strcmp (ustring, str);

if (v == 0)
{
printf ("<%s> equals <%s>.\n", ustring, str);
}
printf("previous string is: %s \n", str);
prvstring[STRSIZE] = str[STRSIZE];
printf("new string is: %s\n", prvstring[STRSIZE]);
}
fclose(pf); /*close file*/
return 0;
}

You need to use strcpy():

Code:

strcpy(prvstring, str);

thank you... I try your method and I got an error saying "segmentation fault (core dumped)" This is what the revised code looks like:

Code:

#include<stdio.h>
#include<string.h>

int main(void)
{
  #define STRSIZE 20
  FILE *pf;
  char str[STRSIZE];  /*Maximum size of a string is 20*/
  char ustring[STRSIZE];
  char *chpoint;
  char *prvstring;

  pf = fopen("input.txt","r");

  if (!pf)
  {
    printf("Can't open the file\n");
    return 0;
  }

  printf("Enter a string. ");
  chpoint = strchr(ustring, '\n');  /*searches for "\n", address is returned if found; otherwise NULL is returned*/

  if (chpoint != NULL)
  {
    *chpoint = 0;   /*removes the \n*/
  }

  while (fscanf(pf, "%s",str) == 1) /*continue to scan and print strings until the EOF*/
  {
    int v = strcmp (ustring, str);

    if (v == 0)
    {
      printf ("<%s> equals <%s>.\n", ustring, str);
    }
    printf("previous string is: %s \n", str);
    strcpy(prvstring, str);
    printf("new string is: %s\n", prvstring);
  }
  fclose(pf);  /*close file*/
  return 0;
}

Do you know why is it doing that?

Thanks

Originally Posted by xp5

Do you know why is it doing that?

Because prvstring is an uninitialized pointer. You either need to allocate memory for it to point to with malloc(), or declare it as a real array, not just a pointer.

Code:

chpoint = strchr(ustring, '\n');  /*searches for "\n", address is returned if found; otherwise NULL is returned*/

ustring is not initialized.

Hi "ustring" is initialize as "char ustring[STRSIZE]". Am I supposed to do it differently?

I modified the code into using array now, but I can't get it to work, it says : "hw1n2.c:38: warning: passing arg 1 of `strcpy' makes pointer from integer without a cast"

I'm not sure on how to fix this problem, the following is my revised code:

Code:

#include<stdio.h>
#include<string.h>

int main(void)
{
  #define STRSIZE 20
  FILE *pf;
  char str[STRSIZE];  /*Maximum size of a string is 20*/
  char ustring[STRSIZE];
  char *chpoint;
  char prstring[STRSIZE];

  pf = fopen("input.txt","r");

  if (!pf)
  {
    printf("Can't open the file\n");
    return 0;
  }

  printf("Enter a string. ");
  chpoint = strchr(ustring, '\n');  /*searches for "\n", address is returned if found; otherwise NULL is returned*/

  if (chpoint != NULL)
  {
    *chpoint = 0;   /*removes the \n*/
  }

  while (fscanf(pf, "%s",str) == 1) /*continue to scan and print strings until the EOF*/
  {
    int v = strcmp (ustring, str);

    if (v == 0)
    {
      printf ("<%s> equals <%s>.\n", ustring, str);
    }
    printf("previous string is: %s \n", str);
    strcpy(prstring[STRSIZE], str);
    printf("new string is: %s\n", prstring[STRSIZE]);
  }
  fclose(pf);  /*close file*/
  return 0;
}

Thank you for your help!

Originally Posted by robwhit

ustring is not initialized.

That doesn't matter. It's (presumably) big enough to hold the result. prvstring, on the other hand, is just an uninitialized pointer. If only people would indicate which LINE caused the seg fault...

Originally Posted by robwhit

it doesn' t hold a result. If it doesn't have a null terminated element, then it will have an array overrun in strchr.

Didn't look closely enough. Again, perhaps I should sleep!

Hi,

Thank you very much for your help!! I'm done with my homework thanks to you! My final code looks like this:

Code:

#include<stdio.h>
#include<string.h>

int main(void)
{
  #define STRSIZE 20
  FILE *pf;
  char str[STRSIZE];  /*Maximum size of a string is 20*/
  char ustring[STRSIZE]={0};
  char *chpoint;
  char prstring[STRSIZE];

  pf = fopen("input.txt","r");

  if (!pf)
  {
    printf("Can't open the file\n");
    return 0;
  }

  printf("Enter a string. ");
  fgets(ustring, STRSIZE, stdin);
  chpoint = strchr(ustring, '\n');  /*searches for "\n", address is returned if found; otherwise NULL is returned*/

  if (chpoint != NULL)
  {
    *chpoint = 0;   /*removes the \n*/
  }

  while (fscanf(pf, "&#37;s",str) == 1) /*continue to scan and print strings until the EOF*/
  {
    int v = strcmp (ustring, str);

    if (v == 0)
    {
      printf("the output is: %s %s\n", prstring, str);
    }
    strcpy(prstring, str);
  }
  fclose(pf);  /*close file*/
  return 0;
}

THANKS!!

you really ought to initialize prstring like brewbuck said, too.