help please!

[idikoko]

why does this not compile?

std::string test;
std::string tester="integer is a number";
int strlen = tester.length() ;
for(int i = 0; i<strlen-1;i++)
{
test[i]=tester[i];
if(test=="integ er")
{cout<<"integer found!";}
}

I am trying to pull extract individual words from a sentence.

[John Harrison]

Re: help please!

idikoko wrote:[color=blue]
> why does this not compile?
>
> std::string test;
> std::string tester="integer is a number";
> int strlen = tester.length() ;
> for(int i = 0; i<strlen-1;i++)
> {
> test[i]=tester[i];
> if(test=="integ er")
> {cout<<"integer found!";}
> }
>
> I am trying to pull extract individual words from a sentence.
>[/color]

I can't see any reason that would not compile. If you are getting
compilation errors then you should quote the error messages you get and
the lines they apply to.

However I can see why the code would not work. This line

test[i]=tester[i];

is wrong because test is a string with zero length, so test[i] is trying
to access a character in the string that doesn't exist. Instead you want

test.push_back( tester[i]);

push_back adds a character to the end of a string.

John

[meagar]

Re: help please!

For future questions, it would help to include the error message your
compiler is giving you.

At a glance, I'd guess you might be redefining 'strlen', which is
already a standard function for finding the length of c-style strings.

Also, while it won't cause a compiler error, the line "test[i] =
tester[i]" is a serious logic error. The [] operator only provides
unchecked access and doesn't itself grow the string to provide storage
for random assignment. You might try test += test[i], which will grow
the test string dynamically by one character each time through the loop.

[John Harrison]

Re: help please!

meagar wrote:[color=blue]
> For future questions, it would help to include the error message your
> compiler is giving you.
>
> At a glance, I'd guess you might be redefining 'strlen', which is
> already a standard function for finding the length of c-style strings.
>[/color]

That won't cause a compile error. The local name will just hide the
global one.

john

[idikoko]

Re: help please!

I got this new error when I used the push_back function.

'std::basic_str ing<_Elem,_Trai ts,_Ax>::push_b ack' : cannot convert
parameter 1 from 'std::string' to 'char'
with
[
_Elem=char,
_Traits=std::ch ar_traits<char> ,
_Ax=std::alloca tor<char>
]

[Ian]

Re: help please!

idikoko wrote:[color=blue]
> I got this new error when I used the push_back function.
>
> 'std::basic_str ing<_Elem,_Trai ts,_Ax>::push_b ack' : cannot convert
> parameter 1 from 'std::string' to 'char'
> with
> [
> _Elem=char,
> _Traits=std::ch ar_traits<char> ,
> _Ax=std::alloca tor<char>
> ]
>[/color]
Quote your code, did you type it correctly? Looks like you may have
left off the [i]

Ian

[idikoko]

Re: help please!

yeah thanks it worked thanks

[Old Wolf]

Re: help please!

John Harrison wrote:[color=blue]
> meagar wrote:[color=green]
>> For future questions, it would help to include the error message your
>> compiler is giving you.
>>
>> At a glance, I'd guess you might be redefining 'strlen', which is
>> already a standard function for finding the length of c-style strings.[/color]
>
> That won't cause a compile error. The local name will just hide the
> global one.[/color]

I think the names of C standard library functions are all reserved
identifiers at any scope. This is in case the standard library
functions are implemented with macros, eg:

#define strlen(s) ( find_eos(s) - (s) )

I can't find exact wording to support this, but N869 7.1.4#1 says:
"Any function declared in a header may be additionally
implemented as a function-like macro defined in the header"