remove first character from line

This is a discussion on remove first character from line within the C++ Programming forums, part of the General Programming Boards category; How would I remove the first character from each line of a file? I put each line into temp and ...

  1. #1
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    remove first character from line

    How would I remove the first character from each line of a file?
    I put each line into temp and try to change the first character but it tells me that I can't convert from "const char" to "char".

    Code:
    #include <iostream>
    #include <fstream>
    
    using namespace std;
    
    int main(void)
    {
        ifstream file;
        ofstream out;
    
        file.open("first.txt");
        out.open("temp.txt");
    
        string temp;
    
        while(file.good())
        {
            getline(file, temp);
    
            temp[0] = ""; //doesn't work
            out << temp << endl;
        }
    
        out.close();
        file.close();
    
        cin.get();
        return 0;
    }

  2. #2
    and the hat of sweating
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    Use the string::erase() member function.
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  3. #3
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    thanks.

    it seems to work now after changing
    Code:
    temp = "";
    to

    Code:
    temp.erase(0,1);

  4. #4
    Always learning
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    Code:
    temp[0] = '\0';
    This will produce no syntax errors.

    Anything contained within "quotes" can be considered as a char* pointer, even if there's a single character in it. So, by putting temp[0] = ""; you basically tried to assign a char* pointer to something that expected a character.

    You should use the functions already described to you, if they do the trick, but I believe it's even more important to understand why the compiler is complaining.

    Try this code for an example:
    cout << (int) "a" << endl;
    cout << (int) 'a' << endl;
    cout << (int) "" << endl;
    cout << (int) '\0' << endl;

  5. #5
    بابلی ریکا Masterx's Avatar
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    Quote Originally Posted by Mr.Pointer View Post
    Code:
    temp[0] = '\0';
    This will produce no syntax errors.

    Anything contained within "quotes" can be considered as a char* pointer, even if there's a single character in it. So, by putting temp[0] = ""; you basically tried to assign a char* pointer to something that expected a character.

    You should use the functions already described to you, if they do the trick, but I believe it's even more important to understand why the compiler is complaining.

    Try this code for an example:
    cout << (int) "a" << endl;
    cout << (int) 'a' << endl;
    cout << (int) "" << endl;
    cout << (int) '\0' << endl
    ;
    will these actually work in C++? i thought (int) var stuff belongs to C! and type casting in C++ differs actually!
    Code:
     static_cast<int> (sth)
    i'd be very thankful if you or anyone else can make it clearer .
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  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by Mr.Pointer
    This will produce no syntax errors.
    It will also do the wrong thing since temp is a std::string object. Actually, even if temp was a null terminated string, assigning a null character to the first character will just truncate the string to zero length instead of removing the first character. The solution that not_someguy eventually used is correct.

    Quote Originally Posted by Mr.Pointer
    Anything contained within "quotes" can be considered as a char* pointer, even if there's a single character in it. So, by putting temp[0] = ""; you basically tried to assign a char* pointer to something that expected a character.
    Loosely speaking, that is true, but technically "" is a const char[1], not a char*.

    Quote Originally Posted by Masterx
    will these actually work in C++? i thought (int) var stuff belongs to C! and type casting in C++ differs actually!
    I recommend the use of the appropriate cast like static_cast in C++, but otherwise the C-style casts still work in C++.
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  7. #7
    Always learning
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    It will also do the wrong thing since temp is a std::string object
    Yeah, like I said, he should use the functions suggested to him. I just thought it would be very important to understand just why it produced a syntax error.

    Loosely speaking, that is true, but technically "" is a const char[1], not a char*.
    Not that it changes anything in the long run, but thanks for the clarification

    I recommend the use of the appropriate cast like static_cast in C++, but otherwise the C-style casts still work in C++.
    I only recently migrated to C++ after having a basic knowledge of C, and I'm still using C-style casting. Thank you for your suggestion, I will look into it.

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