Thread: opening a user selected file

i'm learning how to use files in C...

now, when i want to open user selected file, i can write something like this:
this program opens a user selected file and prints it out on the screen.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

main()
{
	char input[50];
	FILE* f1;
	char out;
	while(1)
	{
		printf("enter filename (up to 50 chars): ");
		gets(input);
		f1=fopen(input,"r");
		printf("\n");
		if(f1)
		{	
			while ((out = fgetc(f1)) != EOF)
			    printf("%c",out);
			printf("\n------------------------------------------------------------\n");
		}
	}
}

the problem which this is that the user has to input 'filename.txt' instead of just 'filename'

i thought of just adding .txt to the string manually and then calling fopen but that seems like the dumb way to go about it.
.
can i somehow add the .txt to the argument without adding it to the string ?

no, it wouldn't be so bad...
i was just wantering if i could somhow add the format to the argument without adding it to the string.
.
maybe something like:

f1=fopen("%s.txt",input,"r");

when input is the formatless filename.
this syntax doesn't work, or i wouldn't have to ask.
but which syntax does ?
can it even be done ?
.
i'm writing this for a university course...
usually i wouldn't use an unsafe function like gets(), but since i am to assume all input is valid, i don't really see the point.
.
as for the implicit main...
i heard that's a problem, but that's how i learned and it doesn't seem to cause any trouble.

i thought of just adding .txt to the string manually and then calling fopen but that seems like the dumb way to go about it.
.
can i somehow add the .txt to the argument without adding it to the string ?

How else would you do it? There is nothing built into any of the standard libraries that magically knows you want to append ".txt" onto your filename.

Also, read the manual on fgetc, in particular paying attention to the return type/value.

First of all please make sure that you follow what the forum members are trying to say to you.

i'm writing this for a university course...
usually i wouldn't use an unsafe function like gets(), but since i am to assume all input is valid, i don't really see the point.
.
as for the implicit main...
i heard that's a problem, but that's how i learned and it doesn't seem to cause any trouble.

main is not supposed to be used like that and so is the gets() . There are other functions which can be used like scanf. And as was pointed out earlier make use of strcat() which adds two strings.

[insert]

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
	char input[50];
	FILE* f1;
	char out;
	while(1)
	{
		printf("enter filename (up to 50 chars): ");
		//gets(input);
		scanf("%s", input);
		strcat(input,".txt");
		f1=fopen(input,"r");
		printf("\n");
		if(f1)
		{	
			while ((out = fgetc(f1)) != EOF)
			    printf("%c",out);
			printf("\n------------------------------------------------------------\n");
		}
	}
	return 0;
}

Thanks @above,

Now i think i ll make sure that i give the buffer size when i use scanf till the time i become comfortable with using fgets.

PS:
The program above which i used can be given with just the filename without appending the .txt . It works as in the next line i call strcat to append .txt to the filename before actually opening the file.

Looks like you want to use formatting convention to fill out the file name. Something like:

Code:

char temp_buf[300];
...
sprintf(temp_buff, "%s.txt", input); 
f1=fopen(temp_buf, "r");

Originally Posted by nonoob

Looks like you want to use formatting convention to fill out the file name. Something like:

Code:

char temp_buf[300];
...
sprintf(temp_buff, "%s.txt", input); 
f1=fopen(temp_buf, "r");

Just to be safe check that sprintf returns a values <= 300. Or make use of snprintf.

Good point. I was relying on the max file/folder name length type things. But ya never know what a crazily flailing user might do when given an input prompt. Those darn pesky users!