c variadic functions, same arguments, different formats

Question

I'm having a problem with va_ methods, and I couldn't find an example (or didn't figure out what the keywords are). The problem is, I need to use the same args for different formats, but the compiler gives me:

incorrect usage of va_start

error. The code I'm trying is something like this:

void vSaveNecessaryFields(EnumA eFormat, ...)
{
    va_list xArgs, xArgs2;
    const char *fmt1 = NULL, *fmt2 = NULL;
    char caString[100] = {0};

    fmt1 = cpGetDbFormat(eFormat);
    fmt2 = cpGetPrinterFormat(eFormat);

    va_start(xArgs1, fmt1);
    va_copy(xArgs2, xArgs1);
    vsnprintf(caString, sizeof(caString), fmt1, xArgs1);

    vSaveToDb(caString);

    va_start(xArgs2, fmt2);
    vsnprintf(caString, sizeof(caString), fmt2, xArgs2);
    vPrintFormatted(caString);
    va_end(xArgs2);
    va_end(xArgs1);
}

How can I solve this problem?

va_start(xArgs1, fmt1) --> va_start(xArgs1, eFormat)

LPs
– LPs

2016-10-03 08:51:11 +00:00
Commented Oct 3, 2016 at 8:51 — LPs
– LPs, Commented Oct 3, 2016 at 8:51
trying it now. who downvoted this and why?

Taha Paksu
– Taha Paksu

2016-10-03 08:57:34 +00:00
Commented Oct 3, 2016 at 8:57 — Taha Paksu
– Taha Paksu, Commented Oct 3, 2016 at 8:57
it worked. write it as an answer and I'll accept it.

Taha Paksu
– Taha Paksu

2016-10-03 09:26:07 +00:00
Commented Oct 3, 2016 at 9:26 — Taha Paksu
– Taha Paksu, Commented Oct 3, 2016 at 9:26

chqrlie · Accepted Answer · 2016-10-03 09:32:52Z

2

The argument to va_start should be the eFormat argument. Furthermore, the va_list is declared as xArgs but you use xArgs1, which causes a syntax error.

void vSaveNecessaryFields(EnumA eFormat, ...) {
    va_list xArgs, xArgs2;
    const char *fmt1 = NULL, *fmt2 = NULL;
    char caString[100] = {0};

    fmt1 = cpGetDbFormat(eFormat);
    fmt2 = cpGetPrinterFormat(eFormat);

    va_start(xArgs, eFormat);
    vsnprintf(caString, sizeof(caString), fmt1, xArgs);
    va_end(xArgs);

    vSaveToDb(caString);

    va_start(xArgs2, eFormat);
    vsnprintf(caString, sizeof(caString), fmt2, xArgs2);
    vPrintFormatted(caString);
    va_end(xArgs2);
}

answered Oct 3, 2016 at 9:32

chqrlie

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1 Comment

Taha Paksu Over a year ago

xArgs -> xArgs1 was a typo of mine when I simplified the code :)

Malcolm McLean · Accepted Answer · 2016-10-03 08:51:24Z

0

You need to call va_end, then call va_start a second time after you have closed the parameter block.

answered Oct 3, 2016 at 8:51

Malcolm McLean

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