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modulo_function
Lv 7
modulo_function asked in Computers & InternetProgramming & Design · 1 decade ago

C++, format spec for getting double with scanf(..)?

This code doesn't get num correctly:

double num;

printf("\nEnter the number: ");

scanf("%f",&num);

but changing to

float num;

and it works fine!

What is the format spec for a double? cplusplus.com doesn't have an answer.

Thanks

Update:

Thanks guys. Also, I know that there's a (long double) cast. What's the format spec for printing a long double?

Update 2:

Thanks Cubbi. I always learn a lot from your answers. And yes, C++ is fun! Can you send me a reference to this C standard of which you speak? I use cplusplus.com as my reference and it's either not there or I missed it.

2 Answers

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  • ?
    Lv 7
    1 decade ago
    Favorite Answer

    My compiler helpfully gives a diagnostic on your program:

    test.cc:6:16: warning: format '%f' expects type 'float*', but argument 2 has type 'double*'

    Since this is a C function, the C++ language standard simply refers to the C language standard, which says, under 7.19.6.2:

    l (ell)

    Specifies that [...] a following a, A, e, E, f, F, g, or G conversion specifier applies to

    an argument with type pointer to double

    So, use %lf

  • oops
    Lv 6
    1 decade ago

    "%Lf"

    Long float

    Edit: My mistake, lf is for doubles, LF is for long doubles. Lf worked for me because my compiler doesn't distinguish between the two.

    Lf should work for printing long doubles.

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