read values from a txt file
i know this a very baxic question but i don't have anyone to ask so please take pity on me!
i need to read in a list of numbers from a text file and save them to various variables. my problem isn't in reading the actual numbers in but that i don't know how to make an array of individual numbers represented by characters as one number.
for exp:
char b[]={ 1 , . , 5 , 3 }
but how do i get
double n=1.53
???
or am i going about this all wrong?
Well, I hope I understand your question...it looks to me like you want to read in numbers as represented in a text file and assign them to variables of type double instead of string or char*. The best way I knwo of to do this is to use a file stream, which you can then read from just like cin:
If I am misinterpreting your question, please post again with more details.Code:#include <iostream> #include <fstream> int main() { ifstream inFile("numbers.txt"); double a, b, c; inFile >> a >> b >> c; }
Okay, I know of no standard function to convert strings to doubles. If you know the values won't be floating point, you can use atoi() to convert the string to a number. For example:char b[]={ 1 , . , 5 , 3 }
but how do i get
double n=1.53;
char b[] = {"1234"};
int a = atoi(b);
Edit:: There's also atof() which converts a string into a floating point value. While you won't be getting the extra precision of a double, you can still extract the value from the string. Example:
char b[] = {"1.345"}
float a = atof(b);
Last edited by Eibro; 08-30-2002 at 12:31 PM.
You can use stringstreams to convert from any type to anytype as long as the stream output from one type is readable as stream input from the other type.
Code:#include <sstream> #include <iostream> // generalized notion of stream_casting template <class outType, class inType> outType stream_cast(const inType& in) { outType out; std::ostringstream outStream; outStream << in; std::istringstream inStream(outStream.str()); inStream >> out; return out; } int main() { // specific example of stream casting char numAsChar[]="1.532"; double numAsDouble; std::ostringstream out; out << numAsChar; std::istringstream in(out.str()); in >> numAsDouble; std::cout << numAsDouble << std::endl; // use templated general stream cast numAsDouble = stream_cast<double>(numAsChar); std::cout << numAsDouble << std::endl; return 0; }
thank you so much to all of you that answered!
