assigning a string to a variable

This is a discussion on assigning a string to a variable within the C Programming forums, part of the General Programming Boards category; Hi, I'm currently trying to store a string by using this notation: prvstring[STRSIZE] = str[STRSIZE]. For some reason it doesn't ...

  1. #1
    xp5
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    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;
    }

  2. #2
    Captain Crash brewbuck's Avatar
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    You need to use strcpy():

    Code:
    strcpy(prvstring, str);

  3. #3
    xp5
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    segmentation fault (core dumped)

    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

  4. #4
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by xp5 View Post
    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.

  5. #5
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    Code:
    chpoint = strchr(ustring, '\n');  /*searches for "\n", address is returned if found; otherwise NULL is returned*/
    ustring is not initialized.

  6. #6
    xp5
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    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!

  7. #7
    Madly in anger with you
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    he means that ustring does not actually contain a string.

    you probably want something like:

    Code:
    printf("Enter a string. ");
    scanf("&#37;s", ustring);
    chpoint = strchr(ustring, '\n');  /*searches for "\n", address is returned if found; otherwise NULL is returned*/

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  8. #8
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by robwhit View Post
    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...

  9. #9
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    Quote Originally Posted by brewbuck View Post
    That doesn't matter. It's (presumably) big enough to hold the result.
    it doesn't hold a result. If it doesn't have a null terminated element, then it will have an array overrun in strchr.

    to initialize the array do this:
    Code:
    char ustring[STRSIZE]={0};
    Last edited by robwhit; 08-29-2007 at 11:11 PM.

  10. #10
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by robwhit View Post
    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!

  11. #11
    xp5
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    Thank you!!

    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!!

  12. #12
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    you really ought to initialize prstring like brewbuck said, too.

  13. #13
    CSharpener vart's Avatar
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    you should check the return value of fgets before calling strchr
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