How do you open a file from user input?

**DaNxTh3xMaNx** · 08-29-2010

I need to open a file that will be entered by the user and I don't know how to do this. I tried putting

Code:

ifp= fopen("%s", "r", &filename);

//also tried:

ifp= fopen(filename, "r");

Code:

printf("Enter the name of the file with the ticket data.\n");
    scanf("%s", filename);
   
    FILE *ifp;

so what is the command you use to open a file based on user input that was stored in a variable filename?

**DaNxTh3xMaNx** · 08-29-2010

... got it. why do i always get it right after i ask for help.

i didn't have &filename in my scan i just had filename and then when i used

Code:

    ifp= fopen(filename, "r");

it worked.

but thanks for looking.

**Elysia** · 08-29-2010

This is incorrect.
It should be:

Code:

printf("Enter the name of the file with the ticket data.\n");
if (fgets(filename, sizeof(filename), stdin))
    filename[strlen(filename)] = '\0';
FILE *ifp = fopen(filename, "r");

SourceForge.net: Scanf woes - cpwiki
I also urge you to check your local documentation on fopen. It does not behave like scanf or printf.

Disclaimer: Not tested. Use at your own risk.

**DaNxTh3xMaNx** · 08-29-2010

^^^yea that crashes right after i type in the filename.

is that necessary for a first assignment in computer science 1? it seems a bit over my head.

**Elysia** · 08-29-2010

Yes, because scanf is unsafe.
And for some reason, those who made the standard thought that fgets should leave the newline in the input buffer, making it even more pain.

**Babkockdood** · 08-29-2010

You cannot use %s with fopen. Try something like this.

Code:

char filename[256];
printf("Filename: ");
scanf("%s", &filename);
FILE *in = fopen(filename, "r");
if (in == NULL) printf("File does not exist.\n");
else printf("File exists.\n");

**Bayint Naung** · 08-29-2010

Code:

scanf("%s", &filename);

Question 12.12b

**Elysia** · 08-30-2010

Babkockdood: READ what has already been posted.
You should NOT read strings with scanf for reasons already stated in a link. And passing an array with & is undefined behavior.

**laserlight** · 08-30-2010

Originally Posted by Elysia

And passing an array with & is undefined behavior.

Passing the address of an array to scanf with a corresponding %s format specifier, that is.

Thread: How do you open a file from user input?

Thread Tools

Search Thread

Display

How do you open a file from user input?

Similar Threads

Memory Leak in AppWizard-Generated Code

Data Structure Eror

Totally confused on assigment using linked lists

Need help; stuck with this; read file + compare with user input