I am creating some wrapper functions using vsprintf() function but its failing if column value > 0 .I compiled this code with different complier but getting the same result. You can check result of this code here -> Compiler Explorer

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

#define MAX_ROW 4
#define MAX_COL 16

typedef struct {
union {
        char data[MAX_ROW][MAX_COL];
        char bytes[MAX_ROW * MAX_COL];
    };
 char size;
}M_BUFFER_Typedef;

char M_BufferPrintf(M_BUFFER_Typedef *buffer,const char *fmt,char row,char col,...) {

  if(row > MAX_ROW)
   return 0;

   va_list arg;

   va_start(arg,col);

   vsprintf((char *)&buffer->data[row][col],fmt,arg);

   va_end(arg);

   return 1;
}

int main() {

  M_BUFFER_Typedef buffer = {
     0
  };

  M_BufferPrintf(&buffer,"H : %d %.02f",0,0,5,1.2695);
  M_BufferPrintf(&buffer,"H : %d %.02f",1,2,6,30.2695);
  M_BufferPrintf(&buffer,"H %.02f",2,0,100.2695);
  M_BufferPrintf(&buffer,"H : %d ",3,0,9);

  printf("\n%s",buffer.data[0]);
  printf("\n%s",buffer.data[1]);
  printf("\n%s",buffer.data[2]);
  printf("\n%s",buffer.data[3]);
}

Code output:

> ASM generation compiler returned: 0
> Execution build compiler returned: 0\n
> Program returned: 0

H : 5 1.27
//if col value 2 -> nothing copied here 
H 100.27 
H : 9 

CodePudding user response：

It works fine, nothing is failing - you simply do not understand how it works

The second one does not work as you expect because you print from the first character of row 1 , but vsprintf has written starting from the char number three and the two first characters are still zero.

if you change the line printing it to:

  printf("\n%s",&buffer.data[1][2]);

It will print what you expect there.

You can print the content of the row to see what is there:

  printf("Content of the row 2: "); for(int i =0; i < MAX_COL; i  ) printf("%d ", buffer.data[1][i]);
  printf("\n");

https://godbolt.org/z/nav4EK6WT

As you see the row starts from the null character, thus printf the string outputs nothing.