C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Error : Formal argument requires an lvalue          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Gil Guest Posted: Fri Jan 30, 2004 2:47 pm    Post subject: Error : Formal argument requires an lvalue Can anyone see why I'm getting an error with the following code : void NewData::store(NewDataStruct nd, unsigned long& NewDataID) { OtherData.store(nd, NewDataID); // error in this line // error with NewDataID } void OtherData::store(NewDataStruct nd, unsigned long NewDataID) { .. .. .. } error message is : "src/DataObjects.cpp", line 30: Error: Formal argument _NewDataID of type unsigned& in call to NewData::store(const NewDataStruct&, unsigned&) requires an lvalue. Back to top Phlip Guest Posted: Fri Jan 30, 2004 3:00 pm    Post subject: Re: Error : Formal argument requires an lvalue Gil wrote: Quote: Can anyone see why I'm getting an error with the following code : void NewData::store(NewDataStruct nd, unsigned long& NewDataID) { OtherData.store(nd, NewDataID); // error in this line // error with NewDataID } void OtherData::store(NewDataStruct nd, unsigned long NewDataID) { . . . } error message is : "src/DataObjects.cpp", line 30: Error: Formal argument _NewDataID of type unsigned& in call to NewData::store(const NewDataStruct&, unsigned&) requires an lvalue. How is your compiler expected to guess which version of store() to call where? If you feed it things which could be used as unsigned long& or unsigned long, how does it know which version to call? Write only one version of the function, with either unsigned long& - meaning you intend to change the argument, or unsigned long, meaning you don't. -- Phlip http://www.xpsd.org/cgi-bin/wiki?TestFirstUserInterfaces Back to top Sumit Rajan Guest Posted: Fri Jan 30, 2004 3:22 pm    Post subject: Re: Error : Formal argument requires an lvalue "Gil" <brightoceanlight (AT) hotmail (DOT) com> wrote Quote: Can anyone see why I'm getting an error with the following code : void NewData::store(NewDataStruct nd, unsigned long& NewDataID) { OtherData.store(nd, NewDataID); // error in this line // error with NewDataID } You need to decide whether you want NewDataID to be a const unsigned long&. The error could have occurred due to a situation like this: int test(int& i) //error:needs to be const int& in such a case { return i+1; } int main() { test(2); } If you do need to change the value of the integer: int test(int& i) { i=100; return i; } int main() { int j=34; test(j); } Regards, Sumit. Quote: void OtherData::store(NewDataStruct nd, unsigned long NewDataID) { . . . } error message is : "src/DataObjects.cpp", line 30: Error: Formal argument _NewDataID of type unsigned& in call to NewData::store(const NewDataStruct&, unsigned&) requires an lvalue. Back to top Rob Williscroft Guest Posted: Fri Jan 30, 2004 3:59 pm    Post subject: Re: Error : Formal argument requires an lvalue Gil wrote in news:adc2ca29.0401300647.13304207 (AT) posting (DOT) google.com: Quote: Can anyone see why I'm getting an error with the following code : void NewData::store(NewDataStruct nd, unsigned long& NewDataID) { Whats OtherData here, you use it like its an variable identifier but later I see its a class name. Did you mean to write: OtherData::store( nd, NewDataID ); Quote: OtherData.store(nd, NewDataID); // error in this line // error with NewDataID } void OtherData::store(NewDataStruct nd, unsigned long NewDataID) { . . . } error message is : "src/DataObjects.cpp", line 30: Error: Formal argument _NewDataID of type unsigned& in call to NewData::store(const NewDataStruct&, unsigned&) requires an lvalue. The above message contains: NewData::store(const NewDataStruct&, unsigned&); Which is *not* a declaration you've shown us. It might help if you copy (cut & paste) the actual code into your message, then remove the unnessasery details. Rob. -- http://www.victim-prime.dsl.pipex.com/ Back to top Karl Heinz Buchegger Guest Posted: Fri Jan 30, 2004 4:02 pm    Post subject: Re: Error : Formal argument requires an lvalue Phlip wrote: Quote: Gil wrote: Can anyone see why I'm getting an error with the following code : void NewData::store(NewDataStruct nd, unsigned long& NewDataID) { OtherData.store(nd, NewDataID); // error in this line // error with NewDataID } void OtherData::store(NewDataStruct nd, unsigned long NewDataID) { . . . } error message is : "src/DataObjects.cpp", line 30: Error: Formal argument _NewDataID of type unsigned& in call to NewData::store(const NewDataStruct&, unsigned&) requires an lvalue. How is your compiler expected to guess which version of store() to call where? If you feed it things which could be used as unsigned long& or unsigned long, how does it know which version to call? You may have missed, that both store functions belong to different classes acoriding to the posted code. On the other hand, the posted error message doesn't fit with that. More info from the OP is needed. -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Peter Koch Larsen Guest Posted: Fri Jan 30, 2004 5:24 pm    Post subject: Re: Error : Formal argument requires an lvalue "Gil" <brightoceanlight (AT) hotmail (DOT) com> skrev i en meddelelse news:adc2ca29.0401300647.13304207 (AT) posting (DOT) google.com... Quote: Can anyone see why I'm getting an error with the following code : void NewData::store(NewDataStruct nd, unsigned long& NewDataID) { OtherData.store(nd, NewDataID); // error in this line // error with NewDataID } void OtherData::store(NewDataStruct nd, unsigned long NewDataID) { . . . } error message is : "src/DataObjects.cpp", line 30: Error: Formal argument _NewDataID of type unsigned& in call to NewData::store(const NewDataStruct&, unsigned&) requires an lvalue. The code above is okay. You must have made an error when doing cut&paste. This also explains the error-message, where the signature of NewData::store differs from that of the example. Kind regards Peter Back to top Gil Guest Posted: Sat Jan 31, 2004 10:39 am    Post subject: Re: Error : Formal argument requires an lvalue First off, Thanks very much every one for all the helpful feedback!! I changed the code to remove unnecessary details, but I think the code was changed in the translation. More accurate : void NewData::store(NewDataStruct nd, unsigned long& NewDataID) { od.store(nd, NewDataID); // error in this line // error with NewDataID // od is an instantiation of OtherData // od is private to NewData } void OtherData::store(NewDataStruct nd, unsigned long NewDataID) { .. .. .. } The code in question actually compiles without error on Microsoft Visual C++ 6.0. But I get the error when compiling with SunC++ 5.4. At first I thought the error might be because I am passing NewDataID into NewData::store by reference and then am passing this into od.store not as a reference. Could that cause the error? NewData and OtherData are two different classes. I want the parameter NewDataID to be changed in NewData, but not in OtherData. The error message was strange in that it didn't seem to fit with the code I had. Maybe I should put more of the actual code in. 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