sscanf_ tricky func

This is a discussion on sscanf_ tricky func within the C++ Programming forums, part of the General Programming Boards category; I figured it out by trial. But I dont understand how it works. buff[8] , (sscanf(&buff[0], "%x", &x[i]) reads out ...

  1. #1
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    sscanf_ tricky func

    I figured it out by trial.
    But I dont understand how it works.

    buff[8] , (sscanf(&buff[0], "%x", &x[i]) reads out the 1. row (x)
    buff[9] , (sscanf(&buff[2], "%x", &x[i]) reads out the 2. row (y)

    Code:
    #include<windows.h>
    #include<iostream.h>
    #include<conio.h>
    #include<stdio.h>
    
    int main()
    {
    
    char buff[9] ;
    int i;
    int x[10];
    
    FILE *Hex;
    Hex = fopen("hex.txt","r");  //Liest von hex.txt
    
    clrscr();
      while (i<10 && fgets( buff, sizeof(buff), Hex)!= NULL )
      {
        if (sscanf(&buff[2], "%x", &x[i])==1)
          {
           printf("sscanf=%d  i=%d %x\n",sscanf(buff, "%x", &x[i]) ,i,x[i]);
           i++;
          }
       }
    getch();
    }
    How does buff size affect the outcome?

  2. #2
    and the hat of int overfl Salem's Avatar
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    Show us the text file

    There's no point making buff unnecessarily small
    char buff[BUFSIZ];
    is the usual default

    > How does buff size affect the outcome?
    Lines longer that sizeof(buff)-1 get split into multiple parts, which result in multiple calls to fgets, and more increments to i than you expect.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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