vector 'push_back' problem

Discussion in 'C++' started by Al, Dec 25, 2005.

  1. Al

    Al Guest

    What is the problem with this code? It always crashes at the
    'push_back'. I found that thanks to debugging. Any Ideas?
    Other question: what is a faster way to convert a string to an integer?
    Is there a built-in function to do that?
    Here's the code:

    #include <iostream>
    #include <fstream>
    #include <vector>
    #include <string>
    using namespace std;

    int stringToInt(string text)
    {
    int integer=0, temp=1;
    for (int i=text.size()-1, j=1;i>=0;i--, j++)
    {
    switch (text) {
    case 49:
    integer += temp; break;
    case 50:
    integer += 2 * temp; break;
    case 51:
    integer += 3 * temp; break;
    case 52:
    integer += 4 * temp; break;
    case 53:
    integer += 5 * temp; break;
    case 54:
    integer += 6 * temp; break;
    case 55:
    integer += 7 * temp; break;
    case 56:
    integer += 8 * temp; break;
    case 57:
    integer += 9 * temp; break;
    default: break;
    }
    temp *= 10;
    }
    return integer;
    }

    template<class T>
    void print(vector<T> v)
    {
    for (int i=0; i<v.size(); i++)
    cout << i <<" : "<<v<<endl;
    }

    int main()
    {
    ifstream is("D:/dataa.txt");
    vector<vector<int> > theMat;
    string data = "";
    char c;
    int number;
    for (int i=0;;i++)
    {
    while (is.get(c)) {
    if (c == '\t') theMat.push_back(stringToInt(data));
    //here is the problem: the program crashes
    else if (c == '\n') break;
    else data += c;
    }
    }
    print(theMat[0]);
    /*string test = "132435";
    cout <<stringToInt(test); */

    system("pause");
    return 0;
    }
    Al, Dec 25, 2005
    #1
    1. Advertising

  2. On 25 Dec 2005 12:20:26 -0800, "Al" <> wrote:

    >What is the problem with this code? It always crashes at the
    >'push_back'. I found that thanks to debugging. Any Ideas?
    >Other question: what is a faster way to convert a string to an integer?
    >Is there a built-in function to do that?


    Yes. You want either std::stringstream or the CRT strtod() function.
    The latter is better for sanity-checking of input. The former is
    easier to use.

    >Here's the code:
    >
    >#include <iostream>
    >#include <fstream>
    >#include <vector>
    >#include <string>
    >using namespace std;
    >
    >int stringToInt(string text)


    Since you do not change "text", it should be passed by const
    reference. Otherwise, you are copying it unnecessarily.

    >{
    > int integer=0, temp=1;


    It's considered bad style by many people to declare more than one
    variable on the same line.

    > for (int i=text.size()-1, j=1;i>=0;i--, j++)


    What happens when text.size() == 0?
    What happens when text.size() > 10?
    What happens when text holds non-digit characters?
    What happens when text is negative?
    Where is j used in the loop?

    > {
    > switch (text) {


    This is not necessarily portable code because you are making
    assumptions about the internal representation of the particular
    character encoding used. Better to use something like this:

    case '1':
    integer += temp; break;
    case '2':
    integer += 2 * temp; break;
    // etc.

    Note the single quotes used.

    > case 49:
    > integer += temp; break;
    > case 50:
    > integer += 2 * temp; break;
    > case 51:
    > integer += 3 * temp; break;
    > case 52:
    > integer += 4 * temp; break;
    > case 53:
    > integer += 5 * temp; break;
    > case 54:
    > integer += 6 * temp; break;
    > case 55:
    > integer += 7 * temp; break;
    > case 56:
    > integer += 8 * temp; break;
    > case 57:
    > integer += 9 * temp; break;
    > default: break;
    > }
    > temp *= 10;
    > }
    > return integer;
    >}
    >
    >template<class T>
    >void print(vector<T> v)
    >{
    > for (int i=0; i<v.size(); i++)


    size() returns unsigned. It's a very bad mistake to compare signed
    with unsigned values, even if your compiler lets you do it. Turn up
    your warning level so that you at least get a warning about it here.

    > cout << i <<" : "<<v<<endl;
    >}
    >
    >int main()
    >{
    > ifstream is("D:/dataa.txt");
    > vector<vector<int> > theMat;
    > string data = "";
    > char c;
    > int number;
    > for (int i=0;;i++)
    > {
    > while (is.get(c)) {


    The std::getline() function is much better than reading a file
    character-for-character.

    > if (c == '\t') theMat.push_back(stringToInt(data));
    >//here is the problem: the program crashes


    theMat is a vector of vectors. It was never initialized. Therefore, it
    has no elements, yet you use element 0, therefore it crashes.

    > else if (c == '\n') break;
    > else data += c;
    > }
    > }
    > print(theMat[0]);
    > /*string test = "132435";
    > cout <<stringToInt(test); */
    >
    > system("pause");
    > return 0;
    >}


    --
    Bob Hairgrove
    Bob Hairgrove, Dec 25, 2005
    #2
    1. Advertising

  3. Al

    BobR Guest

    Al wrote in message
    <>...
    >What is the problem with this code? It always crashes at the
    >'push_back'. I found that thanks to debugging. Any Ideas?


    // You need to initialize the vector with a size:
    // here's one way:
    size_t rows(480);
    size_t cols(640);
    vector<vector<int> > theMat( rows, cols);

    size_t row(4);
    size_t col(6);
    theMat.at(row).at(col) = 43; // set 5th row, 7th col to 43
    // unless you are positive the index are not out-of-range
    // you should use the at() to access the vector.

    // another way to do it
    vector<vector<int> > theMat;
    for(size_t i(0); /* you need a way out */ ; ++i){
    std::vector<int> tmp;
    theMat.push_back( tmp ); // each pass add another row.
    while (is.get(c)) {
    if (c == '\t') theMat.at( i ).push_back( FromString<int>(data) );
    // ...... fill in data ....
    } //while()
    if( not is ) break;
    } // for()


    >Other question: what is a faster way to convert a string to an integer?
    >Is there a built-in function to do that?


    There are stringstream ToString() and FromString() templates/methods in some
    FAQs.

    #include <sstream>
    // --- string to any number ---
    template<typename T> T FromString(std::string const &str){
    std::istringstream is(str); T tmp; is >> tmp; return tmp;
    } //FromString()
    // -- use it like this --
    std::string Str("54321");
    int num = FromString<int>(Str);
    double num2 = FromString<double>(Str);

    Heed Mr. Hairgrove's suggestions.

    The comp.lang.c++ FAQ is available at http://www.parashift.com/c -faq-lite/

    [corrections always welcome]
    --
    Bob R
    POVrookie
    BobR, Dec 26, 2005
    #3
  4. Al

    Jim Langston Guest

    "BobR" <> wrote in message
    news:UkKrf.353737$...
    >>Other question: what is a faster way to convert a string to an integer?
    >>Is there a built-in function to do that?

    >
    > There are stringstream ToString() and FromString() templates/methods in
    > some
    > FAQs.
    >
    > #include <sstream>
    > // --- string to any number ---
    > template<typename T> T FromString(std::string const &str){
    > std::istringstream is(str); T tmp; is >> tmp; return tmp;
    > } //FromString()
    > // -- use it like this --
    > std::string Str("54321");
    > int num = FromString<int>(Str);
    > double num2 = FromString<double>(Str);


    Here is the version I use:

    #include <sstream>
    template<typename T, typename F > T StrmConvert( F from )
    {
    std::stringstream temp;
    temp << from;
    T to = T();
    temp >> to;
    return to;
    }

    The advantage of this version is that you can convert from/to std::string
    without problems using your same syntax.

    int num = 12345;
    std::string str("67890");

    std::string str2 = StrmConvert<std::string>( num );
    int num2 = StrmConvert<int>( str );

    You don't have to specify the type to convert from, the template figures
    that out itself (somehow I'm not really positive on the mechanics). You
    just have to specify what you are converting to.
    Jim Langston, Dec 26, 2005
    #4
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Ganesh Gella
    Replies:
    5
    Views:
    1,170
    John Harrison
    Jul 14, 2003
  2. Hitesh Bhatiya
    Replies:
    4
    Views:
    4,520
    John Harrison
    Aug 13, 2003
  3. Avi Bercovich
    Replies:
    5
    Views:
    23,620
    Evan Carew
    Jan 14, 2004
  4. Replies:
    8
    Views:
    1,913
    Csaba
    Feb 18, 2006
  5. JoeC
    Replies:
    5
    Views:
    1,349
Loading...

Share This Page