Eug G Eug G - 1 month ago 6
C Question

Input either from stdin or file , C

I have a program that either reads an input from a file or from the keyboard. I have found a way to decide whether the input should be inserted from a file or from keyboard.

I need to implement that decision with an easy way,as I don't want to copy my code 2 times for each type of input.

I tried something like the code bellow but worked only for an input file (arv == 1) , while it gets segm. fault from stdin

error after debugging for arg == 0

(_IO_fgets (buf=0xbffffaac "\030\031\023", n=100, fp=0x0) at iofgets.c:52)

FILE * fp;
if( arg = 1 )
fp = fopen (operationfile, "r");
fp = stdin ;
while (fgets(buffer,sizeof buffer,fp) != NULL)

Any fast way to do this ?

cxw cxw
if(arg == 1) /* == */

should take care of much of your trouble. arg = 1 sets arg to 1 and always succeeds, so the fp=stdin; branch is never used.

Also, your question doesn't show how arg is assigned. Is it the first parameter of main()? If so, that's usually called argc. If you use the conventional name, other developers will have an easier time understanding your code.


  • As @MayurK points out, using 1 == arg rather than arg == 1 will help the compiler protect you from this.

  • As @EdHeal points out, some compilers have options to check for if(arg=1), since it's rarely what you want. In GCC, -Wint-in-bool-context and -Wparentheses are useful (or, better yet, just fire up -Wall!).