How fix error? (point arithmetics)

This is a discussion on How fix error? (point arithmetics) within the C Programming forums, part of the General Programming Boards category; code: Code: #include <stdlib.h> #include <stdio.h> #include <string.h> int main() { /* initial data */ char *original,*copy; original = calloc(sizeof(char),30); ...

  1. #1
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    Question How fix error? (point arithmetics)

    code:
    Code:
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    
    int
    main()
    {
     /* initial data */
     char *original,*copy;
     original = calloc(sizeof(char),30);
     copy = calloc(sizeof(char),30);
     original = "My original string";
     copy = "It's cheap chines copy :)";
    
     /* output original data */
     printf("Original string: \"%s\"\n",original);
     printf("Copy string: \"%s\"\n\n",copy);
    
     /* do coping strings (copy to original) */
     printf("do coping strings (copy to original)\n\n");
     original = calloc(sizeof(char),30);
     while(*original++ = *copy++);
    
     /* output copies data */
     printf("Original string: \"%s\"\n",original);
     printf("Copy string: \"%s\"\n\n",copy);
    }

    terminal output:
    Code:
    grytskiv@ZXDSL831II:~/arithmetic$ gcc -ansi copy_string.c -o copy_string && ./copy_string
    Original string: "My original string"
    Copy string: "It's cheap chines copy :)"
    
    do coping strings (copy to original)
    
    Original string: ""
    Copy string: "Original string: "%s"
    "
    
    grytskiv@ZXDSL831II:~/arithmetic$




    HOW I CAN GET THIS RESULT IN TERMINAL???
    Code:
    ./copy_string
    Original string: "My original string"
    Copy string: "It's cheap chines copy :)"
    
    do coping strings (copy to original)
    
    Original string: "It's cheap chines copy :)"
    Copy string: "It's cheap chines copy :)"

  2. #2
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    1) You cannot asign strings with the = sign in C ... look into strcpy() and memcpy()
    2) By using the = sign you have reassigned the pointers, leaking the memory from the two calloc() calls
    3) Since you are using calloc() on the same variable twice without first using free() your code is leaking memory
    4) Your while() loop at the end is at risk of a runaway since you are not clearly defining an exit
    5) That same while loop leaves the pointers at the first null it finds (i.e. at the end of the string) thus leaking even more memory and risking a buffer overrun.
    Last edited by CommonTater; 03-13-2011 at 11:13 AM.

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