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Anything wrong

Scheduled Pinned Locked Moved C / C++ / MFC
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  • S Smith

    Then what is the best way to clear the buffer initially?

    :beer:

    W Offline
    W Offline
    Waldermort
    wrote on last edited by
    #6

    Since you are dealing with strings there isn't a need to clear the whole buffer. char x[100] = { 0 }; internally calls memset. In your case it's a waste of (7 or so not including the loop inside memset) CPU cycles. char x[100]; x[0] = 0; initially creates an empty string. Just 1 CPU cycle. But then, calling functions like strcpy and sprintf don't require the buffer to be empty whereas strcat NEEDS a string (empty or otherwise) to append to.

    Waldermort

    S 1 Reply Last reply
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    • W Waldermort

      Since you are dealing with strings there isn't a need to clear the whole buffer. char x[100] = { 0 }; internally calls memset. In your case it's a waste of (7 or so not including the loop inside memset) CPU cycles. char x[100]; x[0] = 0; initially creates an empty string. Just 1 CPU cycle. But then, calling functions like strcpy and sprintf don't require the buffer to be empty whereas strcat NEEDS a string (empty or otherwise) to append to.

      Waldermort

      S Offline
      S Offline
      Smith
      wrote on last edited by
      #7

      whereas strcat NEEDS a string (empty or otherwise) to append to. so I'll have to memset everything to 0 or initialize everything to 0 right?

      :beer:

      W 1 Reply Last reply
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      • S Smith

        whereas strcat NEEDS a string (empty or otherwise) to append to. so I'll have to memset everything to 0 or initialize everything to 0 right?

        :beer:

        W Offline
        W Offline
        Waldermort
        wrote on last edited by
        #8

        No. When dealing with string buffers you only need to set the first char/wchar/tchar to 0. char myString[100]; // Is a buffer of 100 chars the a string may be copied into. strcat( myString, "Hello World!" ); // will fail because the buffer is full of junk. // but strcpy( myString, "World!" ); // will work because it doesn't care what is in the buffer myString[0] = 0; // copies an empty string to the buffer strcat( myString, "Hello World!" ); // appends the string to the empty string ( also sets the character after '!' to \0 or NULL. The new string is actually 13 chars because there is a 0 at the end. On another note. You shouldn't be using those string functions. There are safer versions available: strcpy_s( myString, 100, "Hello World!" ); These check to make sure the buffer is large enough for the string Also, you might want to read up on TCHAR and the unicode/ansi string functions TCHAR myString[100]; _tcscpy_s( myString, 100, _T("Hello World!");

        Waldermort

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        • S Smith

          The first yes makes me not to click on the x of this window. Could you please tell me what is wrong with the code before I click on x?

          :beer:

          L Offline
          L Offline
          Luc Pattyn
          wrote on last edited by
          #9

          Smith# wrote:

          char chz[4]={0};

          this buffer is too small, your sprintf statement may generate a minus sign, three digits, a space, and a NULL, that is 6 characters. 60 of these could take up to 301 chars, so char szLogBuff [512]={0}; is sufficiently large, and as others already pointed out, your total initialization is a waste, as each strcat will move the initial terminating NULL backwards. BTW: you could get the correct result with less code, and save some cycles, and never have the bug you had, by having sprintf() fill the final buffer right away; all it takes is a variable pointer as the destination, initialized to szLogBuff, and incremented by the return value of sprintf! :)

          Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

          Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

          CPalliniC 1 Reply Last reply
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          • CPalliniC CPallini

            The code (albeit not beautiful) is correct. With szLogBuf[512]={0}; you actually initialize the whole buffer with 0 (that is '\0'). :)

            If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
            This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
            [My articles]

            L Offline
            L Offline
            Luc Pattyn
            wrote on last edited by
            #10

            CPallini wrote:

            The code ... is correct.

            :thumbsdown:

            Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

            Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

            CPalliniC 1 Reply Last reply
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            • L Luc Pattyn

              CPallini wrote:

              The code ... is correct.

              :thumbsdown:

              Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

              Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

              CPalliniC Offline
              CPalliniC Offline
              CPallini
              wrote on last edited by
              #11

              It isn't wrong. It isn't elegant nor optimal, but not wrong. I think this is a great achievement, after all. (It's a subliminal suggestion for you: could you please hire the OP?)

              If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
              This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
              [My articles]

              In testa che avete, signor di Ceprano?

              L 1 Reply Last reply
              0
              • L Luc Pattyn

                Smith# wrote:

                char chz[4]={0};

                this buffer is too small, your sprintf statement may generate a minus sign, three digits, a space, and a NULL, that is 6 characters. 60 of these could take up to 301 chars, so char szLogBuff [512]={0}; is sufficiently large, and as others already pointed out, your total initialization is a waste, as each strcat will move the initial terminating NULL backwards. BTW: you could get the correct result with less code, and save some cycles, and never have the bug you had, by having sprintf() fill the final buffer right away; all it takes is a variable pointer as the destination, initialized to szLogBuff, and incremented by the return value of sprintf! :)

                Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

                Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

                CPalliniC Offline
                CPalliniC Offline
                CPallini
                wrote on last edited by
                #12

                Luc Pattyn wrote:

                your sprintf statement may generate a minus sign

                No, it cannot. ;P

                If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
                This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
                [My articles]

                In testa che avete, signor di Ceprano?

                L 1 Reply Last reply
                0
                • CPalliniC CPallini

                  It isn't wrong. It isn't elegant nor optimal, but not wrong. I think this is a great achievement, after all. (It's a subliminal suggestion for you: could you please hire the OP?)

                  If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
                  This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
                  [My articles]

                  L Offline
                  L Offline
                  Luc Pattyn
                  wrote on last edited by
                  #13

                  CPallini wrote:

                  It isn't elegant

                  true.

                  CPallini wrote:

                  nor optimal

                  true.

                  CPallini wrote:

                  not wrong

                  false. see my reply to OP. :)

                  Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

                  Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

                  CPalliniC 1 Reply Last reply
                  0
                  • CPalliniC CPallini

                    Luc Pattyn wrote:

                    your sprintf statement may generate a minus sign

                    No, it cannot. ;P

                    If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
                    This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
                    [My articles]

                    L Offline
                    L Offline
                    Luc Pattyn
                    wrote on last edited by
                    #14

                    from the code snippet I can't tell what the definition of BYTE is, could be signed, could be unsigned; I prepare for the worst. Anyway, it isn't really relevant, the buffer isn't sufficiently large. :)

                    Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

                    Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

                    CPalliniC 1 Reply Last reply
                    0
                    • L Luc Pattyn

                      CPallini wrote:

                      It isn't elegant

                      true.

                      CPallini wrote:

                      nor optimal

                      true.

                      CPallini wrote:

                      not wrong

                      false. see my reply to OP. :)

                      Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

                      Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

                      CPalliniC Offline
                      CPalliniC Offline
                      CPallini
                      wrote on last edited by
                      #15

                      See my reply[^]. :)

                      If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
                      This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
                      [My articles]

                      In testa che avete, signor di Ceprano?

                      1 Reply Last reply
                      0
                      • L Luc Pattyn

                        from the code snippet I can't tell what the definition of BYTE is, could be signed, could be unsigned; I prepare for the worst. Anyway, it isn't really relevant, the buffer isn't sufficiently large. :)

                        Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

                        Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

                        CPalliniC Offline
                        CPalliniC Offline
                        CPallini
                        wrote on last edited by
                        #16

                        You didn't read the snippet, did you? (hint: it _s_prints the index, the BYTE part is completely insignificant). :)

                        If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
                        This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
                        [My articles]

                        In testa che avete, signor di Ceprano?

                        L 1 Reply Last reply
                        0
                        • CPalliniC CPallini

                          You didn't read the snippet, did you? (hint: it _s_prints the index, the BYTE part is completely insignificant). :)

                          If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
                          This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
                          [My articles]

                          L Offline
                          L Offline
                          Luc Pattyn
                          wrote on last edited by
                          #17

                          How silly. So that must be wrong too. :laugh:

                          Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

                          Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

                          CPalliniC 1 Reply Last reply
                          0
                          • L Luc Pattyn

                            How silly. So that must be wrong too. :laugh:

                            Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

                            Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

                            CPalliniC Offline
                            CPalliniC Offline
                            CPallini
                            wrote on last edited by
                            #18

                            :laugh:

                            If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
                            This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
                            [My articles]

                            In testa che avete, signor di Ceprano?

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