问题
I have a C++ program that takes in values and prints out values like this:
getline(in,number);
cout << setw(10) << number << endl;
I have an equivalent C program that takes in values and prints out like so:
fscanf(rhs, "%e", &number);
printf("%lf\n", number);
But while the C++ program prints out, 0.30951 the C program prints out 0.309510. More examples: C++: 0.0956439 C: 0.095644. It seems to print the same results as long as the value is 7 digits long, but if its shorter the 7 digits, it adds an extra 0 at the end. And if its longer than 7 digits, it rounds down to 6 digits. I would like the C results to match the C++ program. Any help would be appreciated.
Thanks.
Note: number is a float and number are read from a file.
回答1:
Take advantage of the length and precision specifiers in C++ iostreams
std::cout.precision(4);
std::cout << std::setw(10) << number << "\n";
回答2:
Take advantage of the length and precision specifiers in C formatted print statements:
printf( "%6.4lf", number );
Prints four decimal places in a "cell" six characters wide.
You can use a wildcard character for either length or precision to provide that value at runtime:
int precision = 4;
printf( "%6.*lf", precision, number );
回答3:
printf("%g\n", number);
Will solve your problem, %lf is used for double, %f is used for float, and %g is used for float when you want to display all the decimal places and cut off zeros.
来源：https://stackoverflow.com/questions/15511276/c-printing-out-float-values