What is the argument for printf that formats a long?

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醉酒成梦
醉酒成梦 2020-11-28 17:50

The printf function takes an argument type, such as %d or %i for a signed int. However, I don\'t see anything for a

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  • 2020-11-28 18:14

    In case you're looking to print unsigned long long as I was, use:

    unsigned long long n;
    printf("%llu", n);
    

    For all other combinations, I believe you use the table from the printf manual, taking the row, then column label for whatever type you're trying to print (as I do with printf("%llu", n) above).

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  • 2020-11-28 18:20

    On most platforms, long and int are the same size (32 bits). Still, it does have its own format specifier:

    long n;
    unsigned long un;
    printf("%ld", n); // signed
    printf("%lu", un); // unsigned
    

    For 64 bits, you'd want a long long:

    long long n;
    unsigned long long un;
    printf("%lld", n); // signed
    printf("%llu", un); // unsigned
    

    Oh, and of course, it's different in Windows:

    printf("%l64d", n); // signed
    printf("%l64u", un); // unsigned
    

    Frequently, when I'm printing 64-bit values, I find it helpful to print them in hex (usually with numbers that big, they are pointers or bit fields).

    unsigned long long n;
    printf("0x%016llX", n); // "0x" followed by "0-padded", "16 char wide", "long long", "HEX with 0-9A-F"
    

    will print:

    0x00000000DEADBEEF
    

    Btw, "long" doesn't mean that much anymore (on mainstream x64). "int" is the platform default int size, typically 32 bits. "long" is usually the same size. However, they have different portability semantics on older platforms (and modern embedded platforms!). "long long" is a 64-bit number and usually what people meant to use unless they really really knew what they were doing editing a piece of x-platform portable code. Even then, they probably would have used a macro instead to capture the semantic meaning of the type (eg uint64_t).

    char c;       // 8 bits
    short s;      // 16 bits
    int i;        // 32 bits (on modern platforms)
    long l;       // 32 bits
    long long ll; // 64 bits 
    

    Back in the day, "int" was 16 bits. You'd think it would now be 64 bits, but no, that would have caused insane portability issues. Of course, even this is a simplification of the arcane and history-rich truth. See wiki:Integer

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  • 2020-11-28 18:22

    %ld see printf reference on cplusplus.com

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  • 2020-11-28 18:26

    I think you mean:

    unsigned long n;
    printf("%lu", n);   // unsigned long
    

    or

    long n;
    printf("%ld", n);   // signed long
    
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  • 2020-11-28 18:27

    I think to answer this question definitively would require knowing the compiler name and version that you are using and the platform (CPU type, OS etc.) that it is compiling for.

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  • 2020-11-28 18:34

    It depends, if you are referring to unsigned long the formatting character is "%lu". If you're referring to signed long the formatting character is "%ld".

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