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  4. A Simple C++ Question.

A Simple C++ Question.

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  • S Sivaraman Dhamodharan

    Have a look at the below code:

    #include "stdafx.h"
    #include "conio.h"

    int _tmain(int argc, _TCHAR* argv[])
    {
    //Snippet 1
    char name[20] = "Some Name";
    printf("%s\n", name);
    name[1] = 'a';
    printf("%s\n", name);

    //Snippet 2
    char \* name2 = "Some Name";
    printf("%s\\n", name2);
    name2\[1\] = 'a';
    printf("%s\\n", name2);
    
    getch();
    return 0;
    

    }

    Why we get Runtime error when we modify name2[1] = 'a';?

    Programming Article

    A Offline
    A Offline
    Albert Holguin
    wrote on last edited by
    #3

    In this case... your definition of name2 is what is referred to as a string literal and points to data that is considered constant. See here[^].

    1 Reply Last reply
    0
    • S Sivaraman Dhamodharan

      Have a look at the below code:

      #include "stdafx.h"
      #include "conio.h"

      int _tmain(int argc, _TCHAR* argv[])
      {
      //Snippet 1
      char name[20] = "Some Name";
      printf("%s\n", name);
      name[1] = 'a';
      printf("%s\n", name);

      //Snippet 2
      char \* name2 = "Some Name";
      printf("%s\\n", name2);
      name2\[1\] = 'a';
      printf("%s\\n", name2);
      
      getch();
      return 0;
      

      }

      Why we get Runtime error when we modify name2[1] = 'a';?

      Programming Article

      M Offline
      M Offline
      Maximilien
      wrote on last edited by
      #4

      You are trying to modify a const char array (pointer). This is not C++. if you were writing proper C++, you would not get those problems (or a lot less likely).

      std::string name = "some name";
      std::cout << name << std::endl;

      std::string name2 = "some name";
      std::cout << name2 << std::endl;

      name2[1] = 'a'; // need to check that the index is within the string size.
      std::cout << name2 << std::endl;

      Watched code never compiles.

      C A 2 Replies Last reply
      0
      • M Maximilien

        You are trying to modify a const char array (pointer). This is not C++. if you were writing proper C++, you would not get those problems (or a lot less likely).

        std::string name = "some name";
        std::cout << name << std::endl;

        std::string name2 = "some name";
        std::cout << name2 << std::endl;

        name2[1] = 'a'; // need to check that the index is within the string size.
        std::cout << name2 << std::endl;

        Watched code never compiles.

        C Offline
        C Offline
        Chuck OToole
        wrote on last edited by
        #5

        Technically, to pick nits, it *is* C++ as C++ is a superset of C. What you are really saying is that it isn't "Object Oriented Programming" which is true, but it is still within the definition of C++.

        J A 2 Replies Last reply
        0
        • M Maximilien

          You are trying to modify a const char array (pointer). This is not C++. if you were writing proper C++, you would not get those problems (or a lot less likely).

          std::string name = "some name";
          std::cout << name << std::endl;

          std::string name2 = "some name";
          std::cout << name2 << std::endl;

          name2[1] = 'a'; // need to check that the index is within the string size.
          std::cout << name2 << std::endl;

          Watched code never compiles.

          A Offline
          A Offline
          Albert Holguin
          wrote on last edited by
          #6

          Agree with Chuck... technically it is C++.

          1 Reply Last reply
          0
          • C Chuck OToole

            Technically, to pick nits, it *is* C++ as C++ is a superset of C. What you are really saying is that it isn't "Object Oriented Programming" which is true, but it is still within the definition of C++.

            J Offline
            J Offline
            jschell
            wrote on last edited by
            #7

            Chuck O'Toole wrote:

            Technically, to pick nits, it *is* C++ as C++ is a superset of C

            Does the newest ANSI C++ standard incorporate the latest ANSI C standard as a subset? Last I heard that was not the case

            C 1 Reply Last reply
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            • C Chuck OToole

              Technically, to pick nits, it *is* C++ as C++ is a superset of C. What you are really saying is that it isn't "Object Oriented Programming" which is true, but it is still within the definition of C++.

              A Offline
              A Offline
              Aescleal
              wrote on last edited by
              #8

              C++98 is not a superset of C90 - especially when you consider const and what happens when you cast away const. C allows modification of literals (string and constants) through pointers while C++ doesn't or rather considers it undefined behaviour.

              C 1 Reply Last reply
              0
              • J jschell

                Chuck O'Toole wrote:

                Technically, to pick nits, it *is* C++ as C++ is a superset of C

                Does the newest ANSI C++ standard incorporate the latest ANSI C standard as a subset? Last I heard that was not the case

                C Offline
                C Offline
                Chuck OToole
                wrote on last edited by
                #9

                The point is, C++ did *not* decommit the "char" data type nor pointers. std::string is *not* the only way to do string manipulation in C++. It may be the perferred way for some people but it's not the only way.

                J 1 Reply Last reply
                0
                • A Aescleal

                  C++98 is not a superset of C90 - especially when you consider const and what happens when you cast away const. C allows modification of literals (string and constants) through pointers while C++ doesn't or rather considers it undefined behaviour.

                  C Offline
                  C Offline
                  Chuck OToole
                  wrote on last edited by
                  #10

                  The point is, C++ did *not* decommit the "char" data type nor pointers. std::string is *not* the only way to do string manipulation in C++. It may be the perferred way for some people but it's not the only way.

                  1 Reply Last reply
                  0
                  • C Chuck OToole

                    The point is, C++ did *not* decommit the "char" data type nor pointers. std::string is *not* the only way to do string manipulation in C++. It may be the perferred way for some people but it's not the only way.

                    J Offline
                    J Offline
                    jschell
                    wrote on last edited by
                    #11

                    Chuck O'Toole wrote:

                    The point is, C++ did *not* decommit the "char" data type nor pointer

                    I was responding to what appeared to be a general comment about the language in general and in its entirety and not just one small part. And that general comment, at this time (new standards), is wrong.

                    C 1 Reply Last reply
                    0
                    • J jschell

                      Chuck O'Toole wrote:

                      The point is, C++ did *not* decommit the "char" data type nor pointer

                      I was responding to what appeared to be a general comment about the language in general and in its entirety and not just one small part. And that general comment, at this time (new standards), is wrong.

                      C Offline
                      C Offline
                      Chuck OToole
                      wrote on last edited by
                      #12

                      Context dude, gotta read comments in the context of the thread

                      J 1 Reply Last reply
                      0
                      • C Chuck OToole

                        Context dude, gotta read comments in the context of the thread

                        J Offline
                        J Offline
                        jschell
                        wrote on last edited by
                        #13

                        Chuck O'Toole wrote:

                        Context dude, gotta read comments in the context of the thread

                        And respond in that context. Since another poster read your response in way similar to the way I read it, it suggests that your response is the one at fault.

                        1 Reply Last reply
                        0
                        • D David Crow

                          It all boils down to the difference between an array and a pointer. For name, you have set aside room for 20 characters (that are initialized to "Some Name"). For name2, you are pointing to a static piece of memory. That memory cannot be changed.

                          "One man's wage rise is another man's price increase." - Harold Wilson

                          "Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

                          "Show me a community that obeys the Ten Commandments and I'll show you a less crowded prison system." - Anonymous

                          S Offline
                          S Offline
                          Sivaraman Dhamodharan
                          wrote on last edited by
                          #14

                          Thanks Crow. That is constant piece of memory.

                          Programming Article

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