find exact string match in C++

Question

Here is the code I used to detect the string in a line from a txt file:

int main()
{
    std::ifstream file( "C:\\log.txt" );

    std::string line;
    while(!file.eof())
    {
        while( std::getline( file, line ) )   
        {
            int found = -1;
            if((found = line.find("GetSA"))>-1)
                std::cout<<"We found GetSA."<<std::endl;
            else if ((found = line.find("GetVol"))>-1)
                std::cout<<"We found GetVol."<<std::endl;
            else if ((found = line.find("GetSphereSAandVol"))>-1)
                std::cout<<"We found GetSphereSAandVol."<<std::endl;
            else
                std::cout<<"We found nothing!"<<std::endl;

        }
    }
    std::cin.get();
}

And here is my log file:

GetSA (3.000000)

GetVol (3.000000)

GetSphereSAandVol (3.000000)

GetVol (3.000000)

GetSphereSAandVol (3.000000)

GetSA (3.00000)

The error is, the program will not go to find "GetSphereSAandVol", because it stops at "GetSA". Obviously, the program thinks "GetSphereSAandVol" contains "GetSA", so it will execute:

if(found = line.find("GetSA"))
    std::cout<<"We found GetSA."<<std::endl;

which is not exactly what I want, because I am expecting the program to execute:

else if (found = line.find("GetSphereSAandVol"))
    std::cout<<"We found GetSphereSAandVol."<<std::endl;

So, anyway I can avoid this? to get what I really want? Thanks a lot.

Answer 1

You misunderstand how find works. Read the documentation.

The conditionals should go like this:

if ((found = line.find("xyz")) != line.npos) { /* found "xyz" */ }

---

I would write your entire program like this:

int main(int argc, char * argv[])
{
    if (argc != 2) { std::cout << "Bad invocation\n"; return 0; }

    std::ifstream infile(argv[1]);

    if (!infile) { std::cout << "Bad filename '" << argv[1] << "'\n"; return 0; }

    for (std::string line; std::getline(infile, line); )
    {
        int pos;

        if ((pos = line.find("abc")) != line.npos)
        {
            std::cout << "Found line 'abc'\n";
            continue;
        }

        if ((pos = line.find("xyz")) != line.npos)
        {
            std::cout << "Found line 'xyz'\n";
            continue;
        }

        // ...

        std::cout << "Line '" << line << "' did not match anything.\n";
    }
}

Answer 2

Two errors, one you asked about and one you didn't.

Your if statements are wrong. You misunderstand how string::find works. This is the correct way

        if ((found = line.find("GetSA")) != string::npos)
           ...
        else if ((found = line.find("GetVol")) != string::npos)
           ...
        etc.

If string::find does not find what it's looking for it returns a special value string::npos. This is what your if conditions should test for.

Second error, lose the while (!file.eof()) loop, it's completely unnecessary.