How to extract and delete the chars in a std::string - c++

Question

Suppose I have this kind of string format:
"<RGB:255,0,0>this text is colored RED.<RGB:0,255,0> While this text is colored GREEN";
I want to extract the values inside the <RGB> i.e 255,0,0 and put it on other variables then delete the chars from '<' to '>'.
My code so far:
//this function is called after the loop that checks for the existence of '<'
void RGB_ExtractAndDelete(std::string& RGBformat, int index, RGB& rgb)
{
int i = index + 5; //we are now next to character ':'
std::string value;
int toNumber;
while (RGBformat[i] != ',')
{
value += RGBformat[i++];
}
++i;
std::stringstream(value) >> toNumber;
rgb.R = toNumber;
value = "";
while (RGBformat[i] != ',')
{
value += RGBformat[i++];
}
++i;
std::stringstream(value) >> toNumber;
value = "";
rgb.G = toNumber;
while (RGBformat[i] != '>')
{
value += RGBformat[i++];
}
++i;
std::stringstream(value) >> toNumber;
value = "";
rgb.B = toNumber;
//I got the right result here which is
//start: <, end: >
printf("start: %c, end: %c\n", RGBformat[index], RGBformat[i]);
//but fail in this one
//this one should erase from '<' until it finds '>'
RGBformat.erase(index, i);
}
If I put the <RGB:?,?,?> on the start of the string, it works but it fails when it finds it next to a non '<' character. Or can you suggest much better approach how to do this?

Answer 1

Use std::str::find to locate the <RGB, :, , and >.
Use std::str::substr to "cut out" the string.
Add if (!std::strinstream(value)>> toNumber) ... to check that the number was actually accepted.
Something like this:
std::string::size_type index = std::RGBformat.find("<RGB");
if (index == std::string::npos)
{
... no "<RGB" found
}
std::string::size_type endAngle = std::RGBformat::find(">", index);
if (endAngle == std::string::npos)
{
... no ">" found...
}
std::string::size_type comma = std::RGBformat.find(",", index);
if (comma == std::string::npos && comma < endAngle)
{
... no "," found ...
}
std::string value = RGBformat.substr(index, comma-index-1);
std::stringstream(value) >> toNumber;
value = "";
rgb.R = toNumber;
std::string::size_type comma2 = std::RGBformat.find(",", comma+1);
if (comma2 == std::string::npos && comma2 < endAngle)
...
Note that this may look a bit clumsier than your current code, but it has the advantage of being a lot safer. If someone passed in "<RGB:55> .... " to your existing code, it would break, because it just keeps going until either you get bored and press a key to stop it, or it crashes, whichever comes first...

Answer 2

If you can use Boost or C++11, this is really the perfect place for regular expressions.
You can match your color specifiers with "\\<RGB:(\\d{1,3}),(\\d{1,3}),(\\d{1,3})\\>" - or if you have C++11 raw string literals, you can write this more readably as R"rx(\<RGB:(\d{1,3}),(\d{1,3}),(\d{1,3})\>)rx".

Answer 3

Parse it with
std::getline
http://en.cppreference.com/w/cpp/string/basic_string/getline
This function accepts a delimiter (e.g. '<' or '>') as third argument.
For an example look at:
Basic C++ program, getline()/parsing a file

Answer 4

Here a modified code I use to extract text from html and retrieve data from html tag when I can't use regexp. Otherwise I advice you to use regular expressions they are much more easier to setup.
In my code I ended my tags with "</>" for the color "<RGB:255,0,0>My text</>".
Hope it would help!
#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
using namespace std;
typedef struct{
string text;
uint8_t r;
uint8_t g;
uint8_t b;
}TextInfo;
vector<TextInfo> vect;
const vector<TextInfo> & extractInfos(const string & str){
string newStr = str;
vect.clear();
do{
TextInfo info;
int index = newStr.find('>');
if(index != -1 && newStr.find('<') == 0){
// We get "<RGB:r,g,b>"
string color = newStr.substr(0,index+1);
// We extract red color
string red = color.substr(color.find(':') + 1, color.find(',') - color.find(':') - 1);
// We get "g,b>"
color = color.substr(color.find(',') + 1, color.length() - color.find(','));
// We extract green color
string green = color.substr(0,color.find(','));
// We extract "b>"
color = color.substr(color.find(',') + 1, color.length() - color.find('>'));
// We get blue color;
string blue = color.substr(0,color.find('>'));
// string to int into a uint8_t
info.r = atoi(red.c_str());
info.g = atoi(green.c_str());
info.b = atoi(blue.c_str());
// We remove the "<RGB:r,g,b>" part from the string
newStr = newStr.substr(index+1,newStr.length()-index);
index = newStr.find("</>");
// We get the text associated to the color just extracted
info.text = newStr.substr(0,index);
// We remove the "</>" that ends the color
newStr = newStr.substr(index+3,newStr.length()-(index+2));
}else{
// We extract the string to the next '<' or to the end if no other color is set
int i = newStr.find('<');
if(i == -1){
i=newStr.length();
}
info.text = newStr.substr(0,i);
info.r = 0;
info.g = 0;
info.b = 0; // No color then we put default to black
// We get the new part of the string without the one we just exctacted
newStr = newStr.substr(i, newStr.length() - i);
}
// We put the data into a vector
vect.push_back(info);
}while(newStr.length() != 0); // We do it while there is something to extract
return vect;
}
int main(void){
vector<TextInfo> myInfos = extractInfos("<RGB:255,0,0>String to red</><RGB:0,255,0>Green string</>Default color string");
for(vector<TextInfo>::iterator itr = myInfos.begin();itr != myInfos.end();itr++){
cout << (*itr).text << endl;
}
return 0;
}