CODEWITHSUNDEEP
cfiledynamicfilenames
samir rai
samir rai

Reputation: 21

passing file name as argument

char fname[256];
printf("Enter file name\n");
scanf("%123s",fname);
strcat(fname,".txt");

FILE *inputf;
inputf=fopen(fname,"w");

if (inputf!=NULL)
    printf("found");
else
    printf("not found");

Mow the problem is that no matter what file name i enter i get a non null pointer.can any one explain why??

Upvotes: 0

Views: 2476

Answers (2)

Pete Wilson
Pete Wilson

Reputation: 8694

Not this: 

char fname[256]; 
printf("Enter file name\n"); 
scanf("%123s",fname); 
strcat(fname,".txt"); F
FILE *inputf; inputf=fopen(fname,"w");  // <--!!!
if (inputf!=NULL) printf("found"); 
else printf("not found");



but this instead:



char fname[256]; 
FILE *inputf; 



inputf=fopen(fname,"w");

printf("Enter file name\n"); 



// you know that you can't ever, EVER use scanf( ) so
// remove this time bomb and use something else
scanf("%123s",fname); 



strcat(fname,".txt"); 
inputf=fopen(fname,"w"); 
if (inputf!=NULL) {
  printf("found"); 
}
else {
  printf("not found");
}

Now, what pointer was not NULL? You could not have compiled the code as you had it, so how do you know what was or was not NULL?

--pete

Upvotes: 0

dappawit
dappawit

Reputation: 12570

fopen(filename,"w") will create a new file. Therefore, if you're entering a legal file name and have proper file system permissions, it should succeed.

If you're trying to open an existing file, use:

fopen(filename, "r")

(Notice the "r" mode, instead of "w".)

Upvotes: 3

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