Using Sprintf With Arguments Just Like İn Vprintf

Question

I try to achieve same thing in vprintf function using sprintf to write into buffer, however I can not do it. What is my mistake?

#include <stdio.h>
#include <stdarg.h>


char latestPrint[1000];
int currentPositionPrint=0;



void WriteFrmtd(char *format, ...) {
   va_list args;
   
   va_start(args, format);
   vprintf(format, args);
   va_end(args);
}

void WriteToPrint(char *format, ...) {
   va_list args;
   
   va_start(args, format);
   currentPositionPrint+=sprintf(currentPositionPrint+latestPrint , format, args);
   va_end(args);
   
}

int main () {
   WriteFrmtd("%d variable argument\n", 1);
   WriteFrmtd("%d variable %s\n", 2, "argumentsqweqweqweqwe");
   
   WriteToPrint("%d variable %s\n", 2, "argumentsqweqweqweqwe");
   
   printf("%s",latestPrint);
   return(0);
}

Output:

1 variable argument
2 variable argumentsqweqweqweqwe
1698242904 variable 1698242904 variable

All [`printf`](https://en.cppreference.com/w/c/io/fprintf) variants have corresponding [`vprintf`](https://en.cppreference.com/w/c/io/vfprintf) functions. — Some programmer dude, Sep 24 '20 at 07:29
Why was this question downvoted? The answer is pretty obvious, but the question is well asked, well formatted and it contains a [mcve] etc... — Jabberwocky, Sep 24 '20 at 08:40
Who knows, everyone has a reason to dislike nowadays, don't they? :) — OsmanBerk, Sep 24 '20 at 08:50

score 2 · Accepted Answer · answered Sep 24 '20 at 07:28

You can use vsprintf (same as vprintf but using an array as output instead of stdout):

void WriteToPrint(char *format, ...)
{
   va_list args;
   
   va_start(args, format);
   currentPositionPrint += vsprintf(latestPrint + currentPositionPrint, format, args);
   va_end(args);
}

Jabberwocky · Answer 2 · 2020-09-24T07:33:49.537

1

You can't use sprintf with variable arguments. You need to use vsprintf instead:

Change:

currentPositionPrint += sprintf(currentPositionPrint+latestPrint , format, args);

to:

currentPositionPrint += vsprintf(currentPositionPrint+latestPrint , format, args);

Free hint: use spaces between operators: foo += bar is more readable than foo+=bar.

edited Sep 24 '20 at 07:33

answered Sep 24 '20 at 07:27

Jabberwocky

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Using Sprintf With Arguments Just Like İn Vprintf

2 Answers2