Can someone please explain strings to me?

This is a discussion on Can someone please explain strings to me? within the C Programming forums, part of the General Programming Boards category; I am really stupid and should have done this long ago. I have had my uni classes and struggled with ...

  1. #1
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    Can someone please explain strings to me?

    I am really stupid and should have done this long ago. I have had my uni classes and struggled with C when it came to strings and pointers after reading the books and googling.

    Anyway, I am very competent at Java, but with C I can't understand strings at all. In Java all you do is
    Code:
    String myString = "blah";
    but in C there is all this stuff with arrays - I really can't get it.

    I know that the string is stored in contiguous form in the computer memory, however, I can't understand much more than that.

    Could some kind soul tell me how to initialise strings in C and (preferably in Lehmann's terms) explain exactly what is happening?

    Cheers!

    PS. I struggled so badly that I failed the coursework for the class and have had to do extra stuff over the summer instead of going out drinking every day.

  2. #2
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    String myString = "blah"; --> char myString[] = "blah";

    Each letter in blah is just a character, the string is a bunch of characters called a array.

    So
    myString[0] = 'b'
    myString[1] = 'l'
    myString[2] = 'a'
    myString[3] = 'h'
    myString[4] = '\0';

    The '\0' marks the end of the string(called NULL). The "'" mark means takes its ASCII vaule, since thats all a char really is. Its one block of memory so it can be read straight threw like a line of skipped threw. The first points to the second wihich pont to the...

    If you wat to work with strings(like adding to them, searching) string.h comes in handy.

    Theres a couple of threads and sites that explains this better, its not that bad.

    I think Java is much worse(to learn) Im still fighting with it....

  3. #3
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    make sure you allocate memory for strings.

    Code:
    char sample[50];
    
    char* sample;
    sample = malloc(50);
    this shows two samples that will both work.

    string literals can be declared but not changed later on.

  4. #4
    Comment your source code! Lynux-Penguin's Avatar
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    in the String class for java, I believe there is a function .toChar() or something. Well what that does is it turns the String into a char[]

    A string in C, is comprised of just an array of characters, there is no class in C.
    >Terminated by a NULL character ('\0')
    >Without the NULL character, it is just an array of characters, C will not recognize it as a String without the NULL
    >Thanks Quzah
    if your a beginner to C, try to avoid dynamic strings (strings where you change the size of it)

    and go ahead and be wasteful of memory like
    Code:
    char myStr[256];
    and to use strings, you can't just say
    myStr = "hi";
    there is a function in string.h to assign Literal strings (strings int he quotes) to the character array
    prototype:
    Code:
    int strcpy(char* destination, char* cpyString);
    lets say you allocate some memory for a string and then you want to put Hello world in it, you can do this many ways, here are some:

    Code:
    1:
      char *str = "Hello, World\n";
    2:
      char str[] = "Hello, World\n";
    3:
      char str[256]; 
      strcpy(str,"Hello, World\n");
    just remember that arrays are treated as pointers and similar. Please read the FAQ for more details.

    -LC
    Last edited by Lynux-Penguin; 08-27-2003 at 02:09 PM.
    Asking the right question is sometimes more important than knowing the answer.
    Please read the FAQ
    C Reference Card (A MUST!)
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  5. #5
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    Saravanan.T.S.
    Beginner.

  6. #6
    ATH0 quzah's Avatar
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    A string in C, is comprised of just an array of characters
    No. This is not a string:
    Code:
    char foo[3] = { 'c', 'a', 't' };
    It has no null terminator, and as such, isn't a string. A string is an array of one or more charactes, terminated by a null. Without the null, it's just an array of characters.

    I know you know the difference, but just to clarify for those who don't.

    Quzah.
    Hope is the first step on the road to disappointment.

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    thanks a lot you guys!

  8. #8
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    Originally posted by quzah
    No. This is not a string:
    Code:
    char foo[3] = { 'c', 'a', 't' };
    It has no null terminator, and as such, isn't a string. A string is an array of one or more charactes, terminated by a null. Without the null, it's just an array of characters.

    I know you know the difference, but just to clarify for those who don't.

    Quzah.
    Of course that is not a string. It is an array of character constants. It would be a string constant if it was a seqence of one or more characters surrounded by double quotes. And then of course if it has the null character at the end (as you mentioned). But technically speaking, a string is an array of characters.
    Last edited by kermit; 08-27-2003 at 06:38 PM.

  9. #9
    Comment your source code! Lynux-Penguin's Avatar
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    That is because the compiler adds a NULL character at the end of the double quotes, not all compilers do this, older C compilers do NOT do this, you have to add the '\0' at the end.

    and a string is NOT technically an array of characters. It is an array of characters with NULL at the end. The standard defines a string as an array of characters that is NULL terminated. In the world of programming, techincalities get sent to /dev/null

    in the older C compilers "cat" was illegal to use as a string. "cat\0" was the way you would have to do it. the NULL is VERY important in C, just dont forget the NULL and you will be alright


    -LC
    Asking the right question is sometimes more important than knowing the answer.
    Please read the FAQ
    C Reference Card (A MUST!)
    Pointers and Memory
    The Essentials
    CString lib

  10. #10
    ... kermit's Avatar
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    Ok, being precise does not hurt I suppose. I realised that a string is an array of characters terminated with NULL - I was not disputing that fact. Just as an aside, and not trying to be smart, how often do you think someone would be using an older compiler that required the insertion of '\0' at the end of a string?

  11. #11
    Comment your source code! Lynux-Penguin's Avatar
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    im sorry, the point I was trying to make was, that it must be made very clear that there is in fact a NULL character at the end of every standard c string.

    and beacuse you don't see the null when you use quotes it must be made very clear (especially to new C programmers) that there is a NULL character.

    -LC
    Asking the right question is sometimes more important than knowing the answer.
    Please read the FAQ
    C Reference Card (A MUST!)
    Pointers and Memory
    The Essentials
    CString lib

  12. #12
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    also never use:
    strcpy
    strcmp

    or functions similar to those. instead use:
    strncpy
    strncmp

    this will aviod buffer overflows (segmentation faults).

  13. #13
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    >this will aviod buffer overflows (segmentation faults)<

    Don't be so sure. strn* functions do not protect agains stupidity :
    Code:
    int main(void)
    {
        char s[5];
    
        strncpy(s, "A", 10);
    }
    $ENV: FreeBSD, gcc, emacs

  14. #14
    & the hat of GPL slaying Thantos's Avatar
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    how often do you think someone would be using an older compiler that required the insertion of '\0' at the end of a string?
    Considering that a good number of students are using a Borland compiler from the 1980s I'd say that there is a good chance.

  15. #15
    Just Lurking Dave_Sinkula's Avatar
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    >NULL character

    [NITPICK]
    NULL, by its C standard definition, is "an implementation-defined null pointer constant" or "[t]he null pointer constant to which the macro NULL expands".

    This may be viewed as mere pedantry -- though it is an FAQ -- but I do think it may be worth pointing out that in C, NULL is implied to be a pointer and not a character. By using "NULL character", it might add to confusion for newcomers to the language, because it can have a distinctly different meaning than "null character", which '\0' represents.
    [/NITPICK]
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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