C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  strcat - strange behavior Goto page 1, 2  Next          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Lilith Guest Posted: Mon Feb 27, 2006 10:06 pm    Post subject: strcat - strange behavior I'm working on a simple piece of code under VC++ 6.0. I've got a char Buffer array into which I copy the contents of an MFC control. The string is properly nul terminated. I use strcat (Buffer, "\r\n") to append a carriage return\line feed to the string before outputting it to a display where I can monitor what's being exchanged with another service. But after the strcat the string in Buffer is terminated, not with \r\n but with a \n and NO nul terminator. The carriage return is dropped completely. If this was output for a text file I'd think it was an expected conversion. But all of this is still in memory. TIA, Lilith Back to top Lilith Guest Posted: Mon Feb 27, 2006 11:06 pm    Post subject: Re: strcat - strange behavior On Mon, 27 Feb 2006 17:08:53 -0500, Victor Bazarov <v.Abazarov (AT) comAcast (DOT) net> wrote: Quote: Lilith wrote: I'm working on a simple piece of code under VC++ 6.0. I've got a char Buffer array into which I copy the contents of an MFC control. You know that MFC is off-topic, right? Just checking. I understand that you're not asking about MFC per se. Even when I'm striving for completeness? Quote: The string is properly nul terminated. I use strcat (Buffer, "\r\n") to append a carriage return\line feed to the string before outputting it to a display Outputting a string to a display is not defined in C++, you know that, right? There is no such thing as "display" in C++. Yes, and once again, the purpose was completeness. I wanted it understood why I was appending the CR\LF combination. Quote: where I can monitor what's being exchanged with another service. But after the strcat the string in Buffer is terminated, not with \r\n but with a \n and NO nul terminator. I think this is covered in the FAQ. See 5.8. The carriage return is dropped completely. If this was output for a text file I'd think it was an expected conversion. But all of this is still in memory. I'll believe you when I see the code. strcpy (Buffer, "MAIL FROM: "); m_From.GetWindowText(Text, 512); // sorry if this is MFC strcat (Buffer, Text); // up to this point the string is nul // terminated // Buffer is passed to a function but is still null // terminated following the call strcat(Buffer, "\r\n"); // after this operation the // string is LF terminated with no // nul Quote: V -- Lilith Back to top Guest Posted: Mon Feb 27, 2006 11:06 pm    Post subject: Re: strcat - strange behavior Lilith wrote: Quote: On Mon, 27 Feb 2006 17:08:53 -0500, Victor Bazarov v.Abazarov (AT) comAcast (DOT) net> wrote: Lilith wrote: I'm working on a simple piece of code under VC++ 6.0. I've got a char Buffer array into which I copy the contents of an MFC control. You know that MFC is off-topic, right? Just checking. I understand that you're not asking about MFC per se. Even when I'm striving for completeness? The string is properly nul terminated. I use strcat (Buffer, "\r\n") to append a carriage return\line feed to the string before outputting it to a display Outputting a string to a display is not defined in C++, you know that, right? There is no such thing as "display" in C++. Yes, and once again, the purpose was completeness. I wanted it understood why I was appending the CR\LF combination. where I can monitor what's being exchanged with another service. But after the strcat the string in Buffer is terminated, not with \r\n but with a \n and NO nul terminator. I think this is covered in the FAQ. See 5.8. The carriage return is dropped completely. If this was output for a text file I'd think it was an expected conversion. But all of this is still in memory. I'll believe you when I see the code. strcpy (Buffer, "MAIL FROM: "); m_From.GetWindowText(Text, 512); // sorry if this is MFC strcat (Buffer, Text); // up to this point the string is nul // terminated // Buffer is passed to a function but is still null // terminated following the call strcat(Buffer, "\r\n"); // after this operation the // string is LF terminated with no // nul What is strlen(Buffer) vs. sizeof(Buffer)? Back to top Lilith Guest Posted: Mon Feb 27, 2006 11:06 pm    Post subject: Re: strcat - strange behavior On 27 Feb 2006 14:43:18 -0800, roberts.noah (AT) gmail (DOT) com wrote: Quote: Lilith wrote: On Mon, 27 Feb 2006 17:08:53 -0500, Victor Bazarov v.Abazarov (AT) comAcast (DOT) net> wrote: Lilith wrote: I'm working on a simple piece of code under VC++ 6.0. I've got a char Buffer array into which I copy the contents of an MFC control. You know that MFC is off-topic, right? Just checking. I understand that you're not asking about MFC per se. Even when I'm striving for completeness? The string is properly nul terminated. I use strcat (Buffer, "\r\n") to append a carriage return\line feed to the string before outputting it to a display Outputting a string to a display is not defined in C++, you know that, right? There is no such thing as "display" in C++. Yes, and once again, the purpose was completeness. I wanted it understood why I was appending the CR\LF combination. where I can monitor what's being exchanged with another service. But after the strcat the string in Buffer is terminated, not with \r\n but with a \n and NO nul terminator. I think this is covered in the FAQ. See 5.8. The carriage return is dropped completely. If this was output for a text file I'd think it was an expected conversion. But all of this is still in memory. I'll believe you when I see the code. strcpy (Buffer, "MAIL FROM: "); m_From.GetWindowText(Text, 512); // sorry if this is MFC strcat (Buffer, Text); // up to this point the string is nul // terminated // Buffer is passed to a function but is still null // terminated following the call strcat(Buffer, "\r\n"); // after this operation the // string is LF terminated with no // nul What is strlen(Buffer) vs. sizeof(Buffer)? sizeof(Buffer) = 512 strlen(Buffer) := 50 Lots of room. -- Lilith Back to top Victor Bazarov Guest Posted: Mon Feb 27, 2006 11:06 pm    Post subject: Re: strcat - strange behavior Lilith wrote: Quote: I'm working on a simple piece of code under VC++ 6.0. I've got a char Buffer array into which I copy the contents of an MFC control. You know that MFC is off-topic, right? Just checking. I understand that you're not asking about MFC per se. Quote: The string is properly nul terminated. I use strcat (Buffer, "\r\n") to append a carriage return\line feed to the string before outputting it to a display Outputting a string to a display is not defined in C++, you know that, right? There is no such thing as "display" in C++. Quote: where I can monitor what's being exchanged with another service. But after the strcat the string in Buffer is terminated, not with \r\n but with a \n and NO nul terminator. I think this is covered in the FAQ. See 5.8. Quote: The carriage return is dropped completely. If this was output for a text file I'd think it was an expected conversion. But all of this is still in memory. I'll believe you when I see the code. V -- Please remove capital As from my address when replying by mail Back to top Guest Posted: Tue Feb 28, 2006 12:06 am    Post subject: Re: strcat - strange behavior Lilith wrote: Quote: What is strlen(Buffer) vs. sizeof(Buffer)? sizeof(Buffer) = 512 strlen(Buffer) := 50 Lots of room. Skirt the issue then, set buffer to all 0 before processing. Then if it fails something is modifying it in a way you are not expecting and you can look for it. Back to top Frank Schmidt Guest Posted: Tue Feb 28, 2006 12:06 am    Post subject: Re: strcat - strange behavior <roberts.noah (AT) gmail (DOT) com> schrieb im Newsbeitrag news:1141081683.584734.323970 (AT) i40g2000cwc (DOT) googlegroups.com... Quote: Lilith wrote: What is strlen(Buffer) vs. sizeof(Buffer)? sizeof(Buffer) = 512 strlen(Buffer) := 50 Lots of room. Skirt the issue then, set buffer to all 0 before processing. Then if it fails something is modifying it in a way you are not expecting and you can look for it. does a strlen of 50 not kinda indicates the real length and that there is a 0 and a wrong "DISPLAY"? Back to top Kaz Kylheku Guest Posted: Tue Feb 28, 2006 12:06 am    Post subject: Re: strcat - strange behavior Lilith wrote: Quote: strcpy (Buffer, "MAIL FROM: "); m_From.GetWindowText(Text, 512); // sorry if this is MFC strcat (Buffer, Text); // up to this point the string is nul // terminated Neither strcpy() nor strcat() have any mechanism to guard against storing more characters than the destination array can hold. Quote: // Buffer is passed to a function but is still null // terminated following the call strcat(Buffer, "\r\n"); // after this operation the // string is LF terminated with no // nul How do you know? Are you by chance relying on the variable inspection window of your debugger? That Microsoft thing has certain issues when it comes to displaying strings. It cuts off strings that are too long, and I think it basically just stuffs the text into its own control, so that \r\n just becomes a line break. I haven't used it in a long time, so I can't quite remember. If you want to be sure what's in that character array, you should convert it yourself to printable form and dump it to a debug trace function. Oh, you do know that C++ has a string class, right? Moreover, you do know that MFC has a CString class? Moreover, you do know that the control you are using has a GetWindowText() overload that will put data into a CString object? void CWnd::GetWindowText(CString& rString) const; Why are you messing around with strcat instead of using the string type provided by the framework in which you are making the GUI? Idiot! Back to top Victor Bazarov Guest Posted: Tue Feb 28, 2006 12:06 am    Post subject: Re: strcat - strange behavior Kaz Kylheku wrote: Quote: Victor Bazarov wrote: Outputting a string to a display is not defined in C++, you know that, right? There is no such thing as "display" in C++. There doesn't have to be, because that's covered in the C standard. Section "5.2.2 Character display semantics" in 9899:1999. :) How is that relevant? AFAIK, C++ Standard only refers to 9899:1990. Back to top Kaz Kylheku Guest Posted: Tue Feb 28, 2006 12:06 am    Post subject: Re: strcat - strange behavior Victor Bazarov wrote: Quote: Outputting a string to a display is not defined in C++, you know that, right? There is no such thing as "display" in C++. There doesn't have to be, because that's covered in the C standard. Section "5.2.2 Character display semantics" in 9899:1999. :) Back to top Daniel T. Guest Posted: Tue Feb 28, 2006 2:06 am    Post subject: Re: strcat - strange behavior In article <08t6025tuhupv5c0e1i2e98aggv9vluho5 (AT) 4ax (DOT) com>, Lilith <lilith (AT) dcccd (DOT) edu> wrote: Quote: I'm working on a simple piece of code under VC++ 6.0. I've got a char Buffer array into which I copy the contents of an MFC control. The string is properly nul terminated. I use strcat (Buffer, "\r\n") to append a carriage return\line feed to the string before outputting it to a display where I can monitor what's being exchanged with another service. But after the strcat the string in Buffer is terminated, not with \r\n but with a \n and NO nul terminator. The carriage return is dropped completely. If this was output for a text file I'd think it was an expected conversion. But all of this is still in memory. TIA, Lilith Lilith, try this: int main() { char buffer[10] = "hello"; strcat( buffer, "\r\n" ); assert( buffer[5] == '\r' ); assert( buffer[6] == '\n' ); assert( buffer[7] == 0 ); cout << "working"; } If "working" doesn't print out, then I'd say your strcat function is broken. -- Magic depends on tradition and belief. It does not welcome observation, nor does it profit by experiment. On the other hand, science is based on experience; it is open to correction by observation and experiment. Back to top Victor Bazarov Guest Posted: Tue Feb 28, 2006 5:06 am    Post subject: Re: strcat - strange behavior Daniel T. wrote: Quote: [..] Lilith, try this: ... after adding this: #include <iostream> #include <cstring> #inlcude <cassert> using namespace std; (it can be enough to add <iostream> only, but to be complete, use all headers necessary). Quote: int main() { char buffer[10] = "hello"; strcat( buffer, "\r\n" ); assert( buffer[5] == '\r' ); assert( buffer[6] == '\n' ); assert( buffer[7] == 0 ); cout << "working"; } If "working" doesn't print out, then I'd say your strcat function is broken. V -- Please remove capital As from my address when replying by mail Back to top Lilith Guest Posted: Tue Feb 28, 2006 6:06 am    Post subject: Re: strcat - strange behavior On 27 Feb 2006 15:17:00 -0800, "Kaz Kylheku" <kkylheku (AT) gmail (DOT) com> wrote: Quote: Lilith wrote: strcpy (Buffer, "MAIL FROM: "); m_From.GetWindowText(Text, 512); // sorry if this is MFC strcat (Buffer, Text); // up to this point the string is nul // terminated Neither strcpy() nor strcat() have any mechanism to guard against storing more characters than the destination array can hold. // Buffer is passed to a function but is still null // terminated following the call strcat(Buffer, "\r\n"); // after this operation the // string is LF terminated with no // nul How do you know? Are you by chance relying on the variable inspection window of your debugger? That Microsoft thing has certain issues when it comes to displaying strings. It cuts off strings that are too long, and I think it basically just stuffs the text into its own control, so that \r\n just becomes a line break. I haven't used it in a long time, so I can't quite remember. If you want to be sure what's in that character array, you should convert it yourself to printable form and dump it to a debug trace function. Oh, you do know that C++ has a string class, right? Yes. Quote: Moreover, you do know that MFC has a CString class? Yes. Quote: Moreover, you do know that the control you are using has a GetWindowText() overload that will put data into a CString object? Yes. And under other circumstances I've used it extensively for getting and setting the text of controls. Quote: void CWnd::GetWindowText(CString& rString) const; Why are you messing around with strcat instead of using the string type provided by the framework in which you are making the GUI? Because the function to which I pass the string specifies a char array. And, yes, I know that CString resolves to a character pointer to the character array. It's not my function but I know that the function ends up outputting the string with more than what I feed it. So I don't trust it not to manipulate the string before using it. So I'm playing it safe. Quote: Idiot! And that's why I don't learn a damn thing. Too many people willing to exercise their expertise muscles for slamming people rather than actually trying to help. It's why I hesitate to ask anything in these forums. It's why I put more detail than some people seem to think I should so I don't get someone who calls me an "idiot" for not being explicit enough. Instead I get chidded for mentioning M*C in my post. Thanks to everyone who tried to help. I'm out of here. Idiot! -- Lilith Back to top Lilith Guest Posted: Tue Feb 28, 2006 6:06 am    Post subject: Re: strcat - strange behavior On Tue, 28 Feb 2006 00:16:48 +0100, "Frank Schmidt" <fs (AT) example (DOT) com> wrote: Quote: roberts.noah (AT) gmail (DOT) com> schrieb im Newsbeitrag news:1141081683.584734.323970 (AT) i40g2000cwc (DOT) googlegroups.com... Lilith wrote: What is strlen(Buffer) vs. sizeof(Buffer)? sizeof(Buffer) = 512 strlen(Buffer) := 50 Lots of room. Skirt the issue then, set buffer to all 0 before processing. Then if it fails something is modifying it in a way you are not expecting and you can look for it. does a strlen of 50 not kinda indicates the real length and that there is a 0 and a wrong "DISPLAY"? No. All my inspection is done in debug mode. I'm looking at the string's individual chars and the indexes for the array. -- Lilith Back to top Kaz Kylheku Guest Posted: Tue Feb 28, 2006 5:06 pm    Post subject: Re: strcat - strange behavior Lilith wrote: Quote: On 27 Feb 2006 15:17:00 -0800, "Kaz Kylheku" <kkylheku (AT) gmail (DOT) com wrote: Why are you messing around with strcat instead of using the string type provided by the framework in which you are making the GUI? Because the function to which I pass the string specifies a char array. And, yes, I know that CString resolves to a character pointer to the character array. It's not my function but I know that the function ends up outputting the string with more than what I feed it. So I don't trust it not to manipulate the string before using it. So I'm playing it safe. Microsoft's CString class supports direct manipulation of the string data. It a function by means of which you can pull out a modifiable buffer. It's different from the char * operator that pulls out a const string implicitly: CString::GetBuffer(int); The parameter lets you specify how big the buffer should be. It seems to be designed for the kind of hack where someone wants to add a bit of data at the end. When you are done fiddling with the buffer, you call CString::ReleaseBuffer(). if you need to do more things with the CString data using its own methods before you destroy it. RTFMSDN. In your case, you can pass in a parameter of 512. (That's Big Enough (TM) for any function that is suspected of adding data beyond the end of the string, right? Haha). 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