How can I alphabetize strings from an array in c++?

Question

I have to write a program that sorts 10 people by height, then by last name. I've got the height down, but i can't get the last name sort to work. I'm trying to use strcmp for it. Any time I try to run it though, it flags an error at the strcmp saying, "[Error] cannot convert 'std::string {aka std::basic_string}' to 'const char*' for argument '1' to 'int strcmp(const char*, const char*)'" I'm using strcmp because this is for a school assignment and I am limited by my knowledge of c++ and what my professor allows us to use

int main()
{
    const int SIZE = 10;
    int count = 0;
    bool flag = true;
    string fileName;
    ifstream inputFile;
    string firstName[SIZE];
    string lastName[SIZE];
    int height[SIZE];

    cin >> fileName;
    inputFile.open(fileName.c_str());

    while(count < 10)
    {
        inputFile >> firstName[count];
        inputFile >> lastName[count];
        inputFile >> height[count];
        count++;
    }
    //Sort based on height
    for(int max = SIZE - 1; max > 0 && flag; max--)
    {
        flag = false;

        for(int line = 0; line < max; line++)
        {
            if(height[line] > height[line + 1])
            {
                swap(height[line], height[line + 1]);
                swap(firstName[line], firstName[line + 1]);
                swap(lastName[line], lastName[line + 1]);
                flag = true;
            }
        }
    }
    //Sort based on last name if heights are equal
    for(int max = SIZE - 1; max > 0 && flag; max--)
    {
        flag = false;

        for(int line = 0; line < max; line++)
        {
            if(height[line] == height[line + 1])
            {
                if(strcmp(lastName[line], lastName[line + 1]) > 0)
                {
                    swap(height[line], height[line + 1]);
                    swap(firstName[line], firstName[line + 1]);
                    swap(lastName[line], lastName[line + 1]);
                    flag = true;
                }
            }
        }
    }

Why use strcmp() for std::strings? One could also ask other questions, such as why arrays instead of standard containers? Why roll your own sort instead of using std::sort? — Fred Larson
– Fred Larson, Commented Nov 25, 2019 at 16:40
Please create a minimal reproducible example Your whole problem can be reduced to 2 lines of code: std::string a = "John", b = "Jane" ; strcmp(a, b); The rest is completely irrelevant to the issue you are asking. — bolov
– bolov, Commented Nov 25, 2019 at 16:42
@FredLarson I'm still fairly new to c++ and this is for a school assignment. I'm just using the methods I've been introduced to so far — SirLazuraz
– SirLazuraz, Commented Nov 25, 2019 at 16:46

Adrian Mole · Accepted Answer · 2019-11-25 16:56:44Z

3

If you insist on using the old strcmp function, then you should pass lastName[line].c_str() and lastName[line+1].c_str()as its argument(s). However, you'd be better off using the std::string::compare() function provided by the STL:

if (lastName[line].compare(lastName[line + 1]) > 0)

This does much the same thing.

Or even simpler (as Fred Larson has suggested):

if (lastName[line] > lastName[line+1])

edited Nov 25, 2019 at 16:56

answered Nov 25, 2019 at 16:42

Adrian Mole

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5 Comments

Fred Larson Over a year ago

Or just if (lastName[line] > lastName[line+1])

Adrian Mole Over a year ago

@FredLarson Shorter and sweeter code, I agree, but it does the same thing. From cppreference on string operators: All comparisons are done via the compare() member function (which itself is defined in terms of Traits::compare())

Fred Larson Over a year ago

No question it does the same thing, but it is shorter and sweeter, as you said. Crucially, I feel it more clearly expresses the intent and is thus more readable.

Adrian Mole Over a year ago

@FredLarson I would add it as an option, but I don't want to steal your thunder! 😊

Fred Larson Over a year ago

There, take my thunder.

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