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POStruggling to understand file pointers?
 

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  1. POStruggling to understand file pointers?
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    <p>Main description of the problem below, where it happens. But simply, I cannot figure out why I get error messages after asking </p> <pre><code>if (outf!=NULL){ printf("Output file already exists, overwrite (y/n):"); scanf("%c",yn); } </code></pre> <p>Where outf is a file pointer to an existing file. Please read description halfway through code.</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;float.h&gt; #include &lt;string.h&gt; int main() { /* Declare file pointer */ FILE *inf; FILE *outf; int linenumber,linecounter=0,linepresent; char filename[21]; char detail[21]; char linedetail[21]; char outfilename[21]; char letter,yn='y'; int position; /*INPUT DETAILS Ask user for file name and line number*/ printf("Please enter an input filename and a linenumber: "); //scan filename to char string and line number to int variable scanf("%s %i",&amp;filename,&amp;linenumber); /*OUTPUT DETAILS Ask user for file name, letter &amp; position, etc*/ printf("Please enter an output filename, a letter and a position:"); scanf("%s %c %i",&amp;outfilename,&amp;letter,&amp;position); /* Open file for reading */ inf=fopen (filename,"r"); outf=fopen(outfilename,"r"); /*check that file exists*/ if (inf!=NULL) { </code></pre> <p>Up until here everything works fine! Then I try to find out if the outf file already exists. If outf points to an existing file, it DOES print "Output file already exists, overwrite (y/n):"</p> <p>HOWEVER, as soon as it prints this I get error windows opening! This is probably an extremely rookie mistake - I'm still learning C. If there is no such file the program completes normally and bypasses the if statement okay.</p> <pre><code> if (outf!=NULL){ printf("Output file already exists, overwrite (y/n):"); scanf("%c",yn); } if (yn=='y'){ /*keep reading to end of file*/ while (feof(inf)==0) { linecounter++; /*read each line and store the line number in detail[WORDS GO HERE]*/ fscanf (inf,"%s", &amp;detail); /*If we reach the line selected by the user*/ if (linecounter==linenumber){ strcpy(linedetail,detail); linepresent=1; } } if (linepresent==0) { printf("File only contains %i lines",linecounter); } } else { exit(1); } } else { printf("Input file not found"); } printf("%s",linedetail); /* close the file */ fclose(inf); fclose(outf); return (0); } </code></pre>
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    1. PO
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      1. PTAnswer
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    1. PTQuestion
    1. USR. Martinho Fernandes
    1. USuser1083734
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
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    2. PO
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    3. PO
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    1. This table or related slice is empty.
    1. CODo not forget the `&`: `scanf("%c", &yn)`
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      1. POStruggling to understand file pointers?
      1. USpmg
    2. COIf you found the offending line...why didn't you just try a much simpler program that said only `int main() { char yn = 'y'; scanf("%c", yn); return 0; }`...and when that crashed post just that? :-/ *(Something to consider for next time, that it's best when questions are reduced to the minimal case that produces the error with everything else taken out.)*
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      1. POStruggling to understand file pointers?
      1. USHostileFork
    3. COthanks, i do need to refine my questioning technique! cheers for everyones patience!
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      1. POStruggling to understand file pointers?
      1. USuser1083734
 

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