Copying part of a std::string to another uninitialised string

Question

I am trying to write a C++ function that splits a std::string containing a URL into its components. I need to copy the components into this structure:

typedef struct urlstruct {
    string protocol;
    string address;
    string port;
    string page;
} urlstruct;

Here is the function so far:

int parseAnnounce2(string announce, urlstruct *urlinfo){
    int i;

    if(announce.find("://") != string::npos){
        // "://" found in string, store protocol
        for(i = 0; i < announce.find("://"); i++){

        }
    } else {
        // No "://" found in string
    }

    return 0;
}

I need to copy the characters before the '://' sequence into the urlinfo->protocol string. What is a good way of doing this?

I know that I can't assign it using the following line of code, because the protocol string has not been initialized to contain that memory.

urlinfo->protocol[i] = announce[i];

Qaz · Accepted Answer · 2012-07-21 17:10:20Z

5

Use std::string::assign. This should work:

if (announce.find ("://") != std::string::npos)
    urlinfo->protocol.assign (announce, 0, announce.find ("://"));
else
    //not found, handle

Or, if you want to store the result of find in a variable to not calculate/type it twice, you could do that too:

std::string::size_type foundPos = announce.find ("://");
if (foundPos != std::string::npos)
    urlinfo->protocol.assign (announce, 0, foundPos);
else
    //not found, handle

edited Jul 21, 2012 at 17:10

answered Jul 21, 2012 at 17:03

Qaz

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4 Comments

Code-Apprentice Over a year ago

You could eliminate the duplicated calls to std::string::find() by storing the value in a variable.

Qaz Over a year ago

@Code-Guru, You could, yes. I'd think the compiler would take care of that, though.

Code-Apprentice Over a year ago

Hmm...that would be interesting to check which compilers, if any, optimize away the function call. Of course, I try not to rely to heavily on compiler optimizations.

Mark B Over a year ago

In order to optimize away the find call the compiler has to be able to assert that it has no side effects.

Mark B · Accepted Answer · 2012-07-21 17:03:30Z

2

std::string::insert should do the job here:

size_t pos = announce.find("://");
if(pos != std::string::npos)
{
    protocol.insert(0, announce, 0, pos);
}

answered Jul 21, 2012 at 17:03

Mark B

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Comments

Code-Apprentice · Accepted Answer · 2013-09-16 08:08:16Z

0

Another option is to use std::string::substr(). You already have all the information needed by this function.

edited Sep 16, 2013 at 8:08

user283145

answered Jul 21, 2012 at 20:59

Code-Apprentice

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