Programming Forums > Application Development > C++

v0id · Feb 3rd, 2007, 6:02 AM

Is the std::string empty - or not?
If we check a string like this

std::string myStr;

if(myStr.empty())
    std::cout << "The string is empty" << std::endl;
else
    std::cout << "The string is not empty" << std::endl;

It of course returns the first message, but if we do like this

(Toggle Plain Text)

for(int i = 0; i <= 50; i++)
{
    if(static_cast<int>(myStr[i]) != 0)
        std::cout << "Index[" << i << "] = " << static_cast<int>(myStr[i]) << std::endl;
}

Then there's is some of them with content. On my computer I get the output

Quote:

Originally Posted by Output

Index[4] = 7
Index[8] = 8
Index[12] = 11
Index[16] = 6
Index[20] = 4
Index[24] = 5
Index[28] = 14
Index[32] = 3
Index[36] = 12
Index[40] = 13
Index[44] = 9
Index[48] = 10

As we can see it jumps four, before it's contains content, why?
How can I competely clear the string? I've tried clear() but it again returns some strange content. I've to clear the string competely, because I've to do actions like myStr[2]++ on empty strings, and it's hard if it contains something...

(Toggle Plain Text)

// This is how it should be...
// myStr[4] = 0;
myStr[4]++;
// myStr[4] = 1;

// This is how it is now...
// myStr[4] = 7;
myStr[4]++;
// myStr[4] = 8;

v0id · Feb 3rd, 2007, 11:25 AM

I've found another solution.
Instead of using an std::string for data, I now use a std::vector.

Eoin · Feb 3rd, 2007, 11:36 AM

Hi v0id, the internal format of a std::string is not specified specifically so you cannot rely on something like say an empty string being 'zero'ed unfortunately. In addition I suspect trying to access index's outside the strings length is very dangerous.

I would advise designing your own simple string class based on your needs, perhaps one which you could convert to and from std::strings as you need. You could use something like std::vector<char> for the memory which would mean you'd know exactly what is going on beneath the surface.

[edit] you beat me to the answer

v0id · Feb 3rd, 2007, 1:22 PM

Quote:

Originally Posted by Eoin

In addition I suspect trying to access index's outside the strings length is very dangerous.

It was exactly because of this reason I choosed a container instead. I'd been on the wrong track all the time, because it was only data I should store, not a specific string - to output, eg.

Thanks for your time and answer. :-)

pegasus001 · Feb 4th, 2007, 2:40 PM

Whats the size() for?

DaWei · Feb 4th, 2007, 5:04 PM

size () is for the size of the string, in characters. It has nothing to do with the size of the class, per se, which has a number of controlling entities. A study (or design) of containers would probably clear up some unwarranted misconceptions.

Feb 3rd, 2007, 11:25 AM	#2
v0id Hobbyist Programmer Join Date: Apr 2006 Posts: 155 Rep Power: 3	I've found another solution. Instead of using an std::string for data, I now use a std::vector. __________________ -- v0id

Feb 3rd, 2007, 11:36 AM	#3
Eoin Hobbyist Programmer Join Date: Jun 2006 Location: Ireland Posts: 152 Rep Power: 3	Hi v0id, the internal format of a std::string is not specified specifically so you cannot rely on something like say an empty string being 'zero'ed unfortunately. In addition I suspect trying to access index's outside the strings length is very dangerous. I would advise designing your own simple string class based on your needs, perhaps one which you could convert to and from std::strings as you need. You could use something like std::vector<char> for the memory which would mean you'd know exactly what is going on beneath the surface. [edit] you beat me to the answer __________________ Visit my website BinaryNotions.

Feb 4th, 2007, 2:40 PM	#5
pegasus001 Hobbyist Programmer Join Date: Nov 2006 Location: 163H Posts: 215 Rep Power: 3	Whats the size() for? __________________ You never test the depth of a river with both feet. The believer is happy. The doubter is wise. Free speech carries with it some freedom to listen. The next generation will always surpass the previous one. It`s one of the never ending cycles of life.

Feb 4th, 2007, 5:04 PM	#6
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	size () is for the size of the string, in characters. It has nothing to do with the size of the class, per se, which has a number of controlling entities. A study (or design) of containers would probably clear up some unwarranted misconceptions. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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Programming Forums > Application Development > C++

std::string is not empty?