Creating an array of Strings

This is a discussion on Creating an array of Strings within the C Programming forums, part of the General Programming Boards category; Hi, In a program I'm writing I am attempting to create an array of Strings which is populated with values ...

  1. #1
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    Question Creating an array of Strings

    Hi,

    In a program I'm writing I am attempting to create an array of Strings which is populated with values from a for loop.

    I've created the toy program below to illustrate the issue I'm having:

    Code:
    void fillPArray() {
      char *pArray[10];
    
      int i;
    
      for (i=0;i < 10;i++) {
        char aString[10];
        sprintf(aString, "%d", i);
        pArray[i] = aString;
      }
    
      for (i=0;i < 10;i++) {
        printf("%s\n", pArray[i]);
      }
    }
    I intended the above code to create a new String for every element of the char pointer array and to print out the values 0 ... 9. Currently it prints out all 9's.

    Could it be that the char array aString is being reinitialised on each entry of the loop, allocating the same memory; hence making all the pointers point to the same memory location?

    Whatever the issue is I can't figure out how to handle this properly.

    Any idea what's going wrong here?

    Thanks,

    Danny

  2. #2
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    Quote Originally Posted by Vegenad View Post
    Could it be that the char array aString is being reinitialised on each entry of the loop, allocating the same memory; hence making all the pointers point to the same memory location?
    Yep! that is exactly what's goin' on.

  3. #3
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    Quote Originally Posted by Vegenad View Post
    Whatever the issue is I can't figure out how to handle this properly.
    Either malloc() new memory for each string (remember to free() it later) or
    Code:
    char aString[10][10];
    sprintf(aString[i], "%d", i);
    pArray[i] = aString[i];
    if you don't mind that the strings gets lost when aString goes out of scope.

  4. #4
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    Ah, wonderful. I didn't even consider explicit memory allocation. I come from a Java background and hence know nothing .

    Thank you very much for your help .

    I've pasted the (I think) working code below just in case it's any help to anybody passing through this thread:

    Code:
    void fillPArray() {
      char *pArray[10];
    
      int i;
    
      for (i=0;i < 10;i++) {
        pArray[i] = malloc(sizeof(char)*3);
        sprintf(pArray[i], "%d", i);
      }
    
      for (i=0;i < 10;i++) {
        printf("%s\n", pArray[i]);
        free(pArray[i]);
      }
    }

  5. #5
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    Just one minor thing to note about your code. But maybe you are already aware of it.
    Code:
    pArray[i] = malloc(sizeof(char)*3);
    3 bytes is not enough to hold the string representation of the maximum value of an int. In this case it is safe to use 3 bytes as long as i never goes above 99 but remember to increase the size if you ever increase the max count of the loop.
    I am note sure, but I think a 32 bit int can hold up to 9 digits in base10.

  6. #6
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    Ah yes, good point. I'll bear that in mind.

    Cheers ,

    Danny

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