sprintf values

This is a discussion on sprintf values within the C Programming forums, part of the General Programming Boards category; Hi, stuck on sprintf again.... Code: #define BUFFER_SIZE 2048 void set_output_field(RecordOut * output, char * text, int field_number) { char ...

  1. #1
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    sprintf values

    Hi,

    stuck on sprintf again....


    Code:
    #define BUFFER_SIZE 2048
    
    void set_output_field(RecordOut * output, char * text, int field_number)
    {
    char buffer[BUFFER_SIZE];
    
    <snip>
    
          case CIRCUIT_LENGTH:
    
    printf("CIRCUIT_LENGTH [%s]\n", text);
    printf("CIRCUIT_LENGTH [%f]\n", atof(text));
    
             sprintf(buffer, "%019.3f", (int)(sizeof(output->circuit_length) - 1), atof(text));
    
    printf("CIRCUIT_LENGTH [%s]\n", buffer);
             break;


    /* OUTPUT */
    CIRCUIT_LENGTH [16.72]
    CIRCUIT_LENGTH [16.720000]
    CIRCUIT_LENGTH [000000000000000.000]



    the only undescribed item is circuit_length which is part of a structure

    Code:
    #define  O_CIRCUIT_LENGTH_LEN  19
    
    typedef struct {
        char country  [O_COUNTRY_LEN];
    
    <snip>
    
        char circuit_length  [O_CIRCUIT_LENGTH_LEN];

    the quantity of characters output is fine, but I am blanking out the value somewhere,



    tia,

  2. #2
    Registered User The Dog's Avatar
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    >> sprintf(buffer, "%019.3f", (int)(sizeof(output->circuit_length) - 1), atof(text));

    Why do you have atof(text) in the argument list?
    Code:
    sprintf( buffer, "%019.3f", (int)(sizeof(output->circuit_length) - 1) );

  3. #3
    ATH0 quzah's Avatar
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    Code:
    sprintf(buffer, "%019.3f", (int)(sizeof(output->circuit_length) - 1), atof(text));
    Why do you have two arguments for your statement here? Note the "%f", followed by an integer and a float. You only have one format specifier, but you have two following arguments.

    I'm surprised you're not getting a warning about that. Anyway, the integer fills the %f requirement, and the second is ignored.

    [edit]
    Ah, beat me to the punch. Anyway, you want one or the other. If you want an integer, don't use %f, use %d, or if you want a floating point number, typecast it to a float or double instead of an integer.
    [/edit]

    Quzah.
    Hope is the first step on the road to disappointment.

  4. #4
    and the hat of wrongness Salem's Avatar
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    Well the number of args you pass to sprintf mis-match the number of conversions.
    If you're looking for a programmable fixed width, then perhaps

    sprintf(buffer, "%*.3f", (int)(sizeof(output->circuit_length) - 1), atof(text));
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  5. #5
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    oh dear,


    I think I'll go back to cabbing


    text is the input value that I want to change, I put (int)(sizeof(output->circuit_length) to ensure that the right amount of space was being used, not realising that 19.3 would do that for me

    this

    Code:
    sprintf(buffer, "%019.3f", atof(text));
    is now fine

    CIRCUIT_LENGTH [16.72]
    CIRCUIT_LENGTH [16.720000]
    CIRCUIT_LENGTH [000000000000016.720]



    thank you all,

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