C ++-使用多重分隔符解析.txt文件，显示字符串

Question

everyone! I'm new to C++, alas I make silly mistakes. This is a snippet of a .txt-file's content:

<tag attr1="value1" attr2="value2" ... >

What I'm trying to accomplish is parsing through the .txt-file, generating the following output:

Tag: tag
name: attr1
value: value1
name: attr2
value: value2

What I've done so far didn't work (my problem is the delimiters):

#include<iostream>
#include <sstream>
#include <string>
#include <vector>
#include <fstream>

using namespace std;

struct tagline{
string tag;
string attributeN;
string attributeV;

};

int main(){
vector<tagline> information;
string line;
tagline t;

ifstream readFile("file.txt");
    while(getline(readFile,line)){
    stringstream in(line);
    getline(in,t.tag);
    getline(in,t.attributeN,'=');
    getline(in,t.attributeV,'"');
    information.push_back(t);

}

vector<tagline>::iterator it = information.begin();

for(; it != information.end(); it++){
cout << "Tag: " << (*it).tag << " \n"
     << "name: " << (*it).attributeN << " \n"
     << "value: " << (*it).attributeV << " \n";

}
return 0;

}

All I get is a plain display of the snippet as it's formatted in the .txt-file:

<tag attr1="value1" attr2="value2" ... >

I would be happy if someone could help. Thank you!

Answer 1

This would be better handled using an HTML/XML parser (depending on what your file actually contains).

That being said, you are not parsing the lines correctly.

Your first call to getline(in,t.tag); is not specifying a delimiter, so it reads the entire line, not just the first word. You would have to use getline(in, t.tag, ' '); instead.

Also, your tags can have multiple attributes, but you are only reading and storing the first attribute, ignoring the rest. You need a loop to read all of them, and a std::vector to store them all into.

Try something more like this instead:

#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <fstream>

using namespace std;

struct tagattribute {
    string name;
    string value;
};

struct tagline {
    string tag;
    vector<tagattribute> attributes;
};

int main() {
    vector<tagline> information;
    string line;

    ifstream readFile("file.txt");
    while (getline(readFile, line)) {
        istringstream in(line);

        tagline t;
        tagattribute attr;

        in >> ws;

        char ch = in.get();
        if (ch != '<')
            continue;

        if (!(in >> t.tag))
            continue;

        do
        {
            in >> ws;

            ch = in.peek();
            if (ch == '>')
                break;

            if (getline(in, attr.name, '=') &&
                in.ignore() &&
                getline(in, attr.value, '"'))
            {
                t.attributes.push_back(attr);
            }
            else
                break;
        }
        while (true);

        information.push_back(t);
    }

    vector<tagline>::iterator it = information.begin();
    for(; it != information.end(); ++it) {
        cout << "Tag: " << it->tag << "\n";

        vector<tagattribute>::iterator it2 = it->attributes.begin();
        for(; it2 != it->attributes.end(); ++it2) {
            cout << "name: " << it2->name << "\n"
            << "value: " << it2->value << "\n";
        }

        cout << "\n";
    }

    return 0;
}

Live demo

Alternatively, consider writing some custom operator>> to help with the parsing, eg:

#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <fstream>

using namespace std;

struct tagattribute {
    string name;
    string value;
};

istream& operator>>(istream &in, tagattribute &attr)
{
    getline(in, attr.name, '=');
    in.ignore();
    getline(in, attr.value, '"');
    return in;
}

struct tagline {
    string tag;
    vector<tagattribute> attributes;
};

istream& operator>>(istream &in, tagline &t)
{
    tagattribute attr;

    in >> ws;

    char ch = in.get();
    if (ch != '<')
    {
        in.setstate(ios_base::failbit);
        return in;
    }

    if (!(in >> t.tag))
        return in;

    do
    {
        in >> ws;

        ch = in.peek();
        if (ch == '>')
        {
            in.ignore();
            break;
        }

        if (!(in >> attr))
            break;

        t.attributes.push_back(attr);
    }
    while (true);

    return in;
}

int main() {
    vector<tagline> information;
    string line;

    ifstream readFile("file.txt");
    while (getline(readFile, line)) {
        istringstream in(line);
        tagline t;     

        if (in >> t)
            information.push_back(t);
    }

    vector<tagline>::iterator it = information.begin();
    for(; it != information.end(); ++it) {
        cout << "Tag: " << it->tag << "\n";

        vector<tagattribute>::iterator it2 = it->attributes.begin();
        for(; it2 != it->attributes.end(); ++it2) {
            cout << "name: " << it2->name << "\n"
            << "value: " << it2->value << "\n";
        }

        cout << "\n";
    }

    return 0;
}

Live demo

Answer 2

Well, I would try to do something like this using this wonderful answer :

struct xml_skipper : std::ctype<char> {
    xml_skipper() : ctype(make_table()) { }
private:
    static mask* make_table() {
        const mask* classic = classic_table();
        static std::vector<mask> v(classic, classic + table_size);
        v[','] |= space;
        v['"'] |= space;
        v['='] |= space;
        v['<'] |= space;
        v['>'] |= space;
        return &v[0];
    }
};

Then, what you can do is just keep reading:

ifstream readFile("file.txt");
while(getline(readFile,line)){
    istringstream in(line);
    in.imbue(std::locale(in.getloc(), new xml_skipper));
    in >> t.tag >> t.attributeN >> t.attributeV;
    information.push_back(t);
}
//...

Do note that this will break if values or attribute names have whitespaces.

---

If you want something more serious, you will need to write lexer, syntax tree builder and semantics tree builder.

---

Full code

#include<iostream>
#include <sstream>
#include <string>
#include <vector>
#include <fstream>
#include <sstream>

using namespace std;

struct tagline{
    string tag;
    string attributeN;
    string attributeV;
};

struct xml_skipper : std::ctype<char> {
    xml_skipper() : ctype(make_table()) { }
private:
    static mask* make_table() {
        const mask* classic = classic_table();
        static std::vector<mask> v(classic, classic + table_size);
        v[','] |= space;
        v['"'] |= space;
        v['='] |= space;
        v['<'] |= space;
        v['>'] |= space;
        return &v[0];
    }
};

int main(){
    vector<tagline> information;
    string line;
    tagline t;
    std::istringstream readFile{"<tag attr1=\"value1\" attr2=\"value2\" ... >"};
    while(getline(readFile,line)){
        istringstream in(line);
        in.imbue(std::locale(in.getloc(), new xml_skipper));
        in >> t.tag >> t.attributeN >> t.attributeV;
        information.push_back(t);
    }


    vector<tagline>::iterator it = information.begin();

    for(; it != information.end(); it++){
        cout << "Tag: " << (*it).tag << " \n"
             << "name: " << (*it).attributeN << " \n"
             << "value: " << (*it).attributeV << " \n";
    }
}

---

Live on Wandbox .

Answer 3

If your input may vary within the boundaries of the xml specification, an XML-parser might be a better approach than parsing the string "manually". Just to show how this could look like, see the following code. It is based on tinyxml2 , which just requires to include a single .cpp / .h -file in your project. You could - of course - also use any other xml libraries; this is just for demonstration purpose:

#include <iostream>
#include "tinyxml2.h"
using namespace tinyxml2;

int main()
{
    const char* test = "<tag attr1='value1' attr2 = \"value2\"/>";
    XMLDocument doc;
    doc.Parse(test);
    XMLElement *root = doc.RootElement();
    if (root) {
        cout << "Tag: " << root->Name() << endl;
        const XMLAttribute *attrib = root->FirstAttribute();
        while (attrib) {
            cout << "name: " << attrib->Name() << endl;
            cout << "value : " << attrib->Value() << endl;
            attrib = attrib->Next();
        }
    }
}