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strcmp help

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Cosa

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strcmp problem

Mar 12th, 2008

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
void ChangeAddress()
{
	char searchaddress;
	char newaddress;
 
	cout << endl;
	cout << "Please enter street name to be changed ";
	cin >> searchaddress;
	for (int i=0; i<numrec; i++)
		{
			if (strcmp(SubscriberID[i].Subscriber_Address.streetname, searchaddress) == 0);
			{		 	 
			cout << "Enter the new street name: ";
			cin >> newaddress;
 
			}
		}	
 
}
void ChangeAddress()
{
	char searchaddress;
	char newaddress;
	
	cout << endl;
	cout << "Please enter street name to be changed ";
	cin >> searchaddress;
	for (int i=0; i<numrec; i++)
		{
			if (strcmp(SubscriberID[i].Subscriber_Address.streetname, searchaddress) == 0);
			{		 	 
			cout << "Enter the new street name: ";
			cin >> newaddress;
			
			}
		}	

}

error: invalid conversion from ‘char’ to ‘const char*’
error: initialising argument 2 of ‘int strcmp(const char*, const char*)'

I get this error wen using "strcmp(SubscriberID[i].Subscriber_Address.streetname, searchaddress) == 0);"

This function is part of a program which enters subrcribers into a file system. This specific function is supposed to edit the address of a subscriber. The subscribers are loaded to the array via input stream, and then the array is saved back to the text file. I can assume that there is no subscribers with any identical information.
searching the net hasnt given me much help, all i have found is that const char* is a pointer. All i want to do is compare the string in the array to the string entered by the user. Then if the string in array is equal to the one entered, i will then enter a new string to replace the one in the array. any ideas?

Last edited by Cosa; Mar 12th, 2008 at 7:39 am.

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bugmenot

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Re: strcmp help

Mar 12th, 2008

it's self-explanatory

"searchaddress" is a character, not a string

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Re: strcmp problem

Mar 12th, 2008

You need to have, e.g.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#define ADDRESS_LEN_MAX 123
char searchaddress[ADDRESS_LEN_MAX] = "";
char newaddress[ADDRESS_LEN_MAX] = "";
#define ADDRESS_LEN_MAX 123
char searchaddress[ADDRESS_LEN_MAX] = "";
char newaddress[ADDRESS_LEN_MAX] = "";

or perhaps use std::string (with appropriate changes to the code)
i.e.

Help with Code Tags

C++ Syntax (Toggle Plain Text)

std::string searchaddress;
std::string newaddress;

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vmanes

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Re: strcmp help

Mar 12th, 2008

Also remove the semicolor ( ; ) at the end of the if statement.

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Cosa

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Re: strcmp help

Mar 12th, 2008

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘2’ to ‘int strcmp(const char*, const char*)’
error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘2’ to ‘int strcmp(const char*, const char*)’

I get this error if i use

std::string searchaddress;
std::string newaddress;

And #define isnt supposed to be used in this program. Any other ideas?

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vmanes

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Re: strcmp help

Mar 12th, 2008

You need to use the c_str( ) method of the string type to get a c-style string for the strcmp function. This method returns a char*.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
std::string searchaddress;
std::string newaddress;
 
if ( strcmp( newaddress.c_str(),  searchaddress.c_str() ) == 0)
std::string searchaddress;
std::string newaddress;

if ( strcmp( newaddress.c_str(),  searchaddress.c_str() ) == 0)

But, as long as you're using string types, just compare them directly!

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
if( searchaddress == newaddress )
if( searchaddress == newaddress )

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Cosa

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Re: strcmp help

Mar 12th, 2008

The compare is more like this

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
strcmp(SubscriberID[i].Subscriber_Address.streetname, searchaddress)
strcmp(SubscriberID[i].Subscriber_Address.streetname, searchaddress)

So its comparing the searchaddress to the address in the array. (To store each users details i made an array of structs of type SubscriberID). Then if they are equal i will enter the new address and then replace the address in the array with the new one entered. So would it work like this?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
 std::string searchaddress;
std::string newaddress;
 
if ( strcmp( SubscriberID[i].Subscriber_Address.streetname, searchaddress.c_str() ) == 0)
 std::string searchaddress;
std::string newaddress;

if ( strcmp( SubscriberID[i].Subscriber_Address.streetname, searchaddress.c_str() ) == 0)

If i use this it compiles and runs, but nothing happens after i type in the address to be searched.

Help with Code Tags

C++ Syntax (Toggle Plain Text)

char * cstr, *searchaddress;

Last edited by Cosa; Mar 12th, 2008 at 6:48 pm.

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vmanes

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Re: strcmp help

Mar 12th, 2008

What is the datatype of .streetname? Perhaps if you posted a larger code segment, showing the class or struct definition(s), we'd clear this up more easily.

Simply declaring char * searchaddress; does not give you any place to store input from the user - you've got to give it some memory. Either with the new operator, or declare it as an char array instead char searchaddress[100];

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littlestone littlestone is offline

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Re: strcmp help

Mar 13th, 2008

Do your address have space? cin can not read a string with space. maybe you should use getline to read the address.

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Cosa

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Re: strcmp help

#10

Mar 13th, 2008

I am not at home at the moment so i cant post any code, however i will try declaring the char as an array. I think i already tried that but im not to sure. Street name is of data type char, but i think it might be declared in this fashion

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
 
char streetname = [30]
 
char streetname = [30]

I will post the whole code when i get the chance

Last edited by Cosa; Mar 13th, 2008 at 1:00 am.

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