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I want to be able to read a full line into a character array using a function.

example input text is:

Schmidt, Helga
Alvarez, Ruben
Zowkowski, Aaron
Huang, Sun Lee
Einstein, Beverly

However, im not sure how to read a full line of characters into the array. I know the delimiter for >> is whitespace, but I'm not sure if I change that delimiter to '\n' if it'd work?

void buildList(char (*array)[25], ifstream& inputFile){
    string line;
    for (int i = 0; i < 5; i++)
        getline(inputFile, line);
        array[i] = line.c_str();     
}

Currently this only reads either a last name or first name into my input instead of the whole line. I'm not sure how I can go about changing this. Thanks.

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7
  • @JoeZ that returns a string, not char* though. Commented Nov 18, 2013 at 16:17
  • Try using getline. Here is how. You can always convert string to char* array. Commented Nov 18, 2013 at 16:17
  • @WorldDominator It takes a string as an output parameter, to be precise. And of course you can always get the cstr of any string. Commented Nov 18, 2013 at 16:20
  • I really would recommend you use the std::string version of getline, but if you absolutely insist on not, there are versions that are members of the streams that work with a raw char buffer here. Commented Nov 18, 2013 at 16:25
  • @Hulk I just edited my code to what I believe you recommended but the compiler gives me the issue of "incompatible types in assignment of 'const char*' to 'char [25]'". I'm not sure if c_str helps me. Commented Nov 18, 2013 at 16:28

2 Answers 2

Reset to default
5

First, you definitely want to use std::string here. Once you do that, you can use std::getline:

std::vector<std::string>
buildList( istream& input )
{
    std::vector<std::string> results;
    std::string line
    while ( std::getline( input, line ) ) {
        results.push_back( line );
    }
}

This will make for much simpler and more robust code.

If you have to use such a broken interface, there is a member function getline:

for ( int i = 0; i != 5; ++ i ) {
    input.getline( array[i], maxLength );
}

Also: a function should never take an std::ifstream& as argument (unless it is going to open or close the file). An std::istream& should be used.

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10 Comments

Thank you James! the input.getline worked splendid. My professor said we should use char ** for this assignment so that's why I did it this way. Also, he has not gone over vectors yet. I'll keep the istream& in mind.
Out of curiosity, where is the memory allocated for array[]? ie. what set up all the char * in the array?
@WorldDominator I susspected something along these lines. Logically, I can't believe that someone would introduce you to declarations along the lines of char (*array)[25] (a pointer to an array of 25 char, or a pointer to the first of many such) before teaching you std::vector and std::string, but I keep seeing it.
@JoeZ At the call site. My guess is that he has something like char data[5][25];, and passes data as an argument. What gets me, however: doing this right (and if that's his data declaration, he's done it right) requires knowing some of the more arcane aspects of the C++ type system. It would be one of the last things I'd teach.
@JamesKanze To be honest, the teacher is very poor at teaching and hasnt been in class for 2 weeks now. I've learned as much as I would have if he had been here though. He said we had to initialize the array to array[5][25] in our main function (I'm using header files). So that's why I passed char (*array) [25].
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1

Use this-

void buildList(char (*array)[25], ifstream& inputFile){
    for (int i = 0; i < 5; i++)
        std::inputFile.getline(array[i],50);
}

The second parameter of getline is the maximum number of characters to write to the character array.

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7 Comments

if I use getline I get the error: no matching function for call to 'getline(std::ifstream&, char [25])'
The function is declared in std namespace.
I'm using namespace std though. Isn't it because instead of a string, I used a char[25]?
Oh yes, I overlooked that, I'll just edit the answer.
This is completely wrong. The getline that takes a char* is a member of std::istream, and must use the member syntax in the call. It also requires a maximum length as a second argument.
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