Compile 2 file commands in one in C

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Hi I'm working on a project in C. I want first to open a file called op.txt read the first num of it using fcanf and put the num into a int. Then I want to use another command to write that num into a different file called o.txt

But How can I use a second File command inside the main function which I use the fopen of the first file?

The code for fprint command is

C

#include <stdio.h> 

main() 
{ 
FILE *fp; 
int a = 1; 
fp = fopen("test.txt", "w+"); 
fprintf(fp, "The int is %d\n", a); 
fclose(fp); 
}

and for fsanf is

C

int t_size; 

FILE * fp;	
fp = fopen ("xxx.txt", "r"); 
fscanf(fp, "%d", &t_size); 
fclose(fp);

Posted 15-Nov-14 23:49pm

GeorgeGkas

Updated 16-Nov-14 1:15am

v4

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Comments

[no name] 16-Nov-14 6:12am

Your first file is: FILE *fp;
Think about to open a second file. For this you need to declare a second file hanlde, e.g.:

FILE *fp_write;
fp_write= fopen(...);

[no name] 16-Nov-14 6:26am

I tried it but din't worked

[no name] 16-Nov-14 6:27am

What does not work? Have a look to the two Solutions, there you will find all what you need.

[no name] 16-Nov-14 6:34am

the solutions work but no in my program. I update the code add the program!

[no name] 16-Nov-14 6:37am

What means "it does not work"? Any error message? Or the result is not what you expect?

Please be more specific.

[no name] 16-Nov-14 6:40am

I don't get the output file in my main program

[no name] 16-Nov-14 6:43am

I think the file is there, but not in the Directory you expect.
1.) Try it with a full filename e.g. c:\temp\myoutput.txt (make sure that c:\temp exists).
2.) Like Garth J Lancaster mentioned in his answer, you do not make any error handling. It is worth to add it.

[no name] 16-Nov-14 6:45am

yes but the program should be able to work on any computer and the output file should be able to created in the exact file where the program.exe is.

[no name] 16-Nov-14 6:52am

This is only for test. Of course you need to make it more flexible for the final Version. Step by step :)

[no name] 16-Nov-14 6:53am

yes but the output don't work. This is what I can't understand.

[no name] 16-Nov-14 6:49am

I made an error code but now here is my problem http://prntscr.com/56wmt4 It doesn't return 0

[no name] 16-Nov-14 6:55am

What is "it"?
The Screenshot does not show any usefull Information related to your Problem.

N.B: Also second solution is worth to accept ;)

[no name] 16-Nov-14 6:59am

it shows that if the file that I want to read doesn't exist it returns me that screenshot issue, but I made an error handler for that. What should I do?

[no name] 16-Nov-14 7:01am

boah....you always mentioned that Output file is the Problem and now it is the Input file?
1.) Implement error handling for each line of file io access, read and write
2.) Accept answer #2 :)

[no name] 16-Nov-14 7:13am

NO I made it work! Thank you anyway!

[no name] 16-Nov-14 7:17am

Use absolute paths for both Input/Output for tests. After you are sure that the logic of your app is ok you can go for flexible paths.

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Garth J Lancaster · Accepted Answer · 2014-11-16T00:10:00

not sure what your issue is - you could do this (separate file handle for reading and writing) :-

C++

#include <stdio.h>

main()
{

int t_size; 
 
FILE *fp_read;	
fp_read = fopen ("xxx.txt", "r"); 
fscanf(fp_read, "%d", &t_size); 
fclose(fp_read);

FILE *fp_write;
int a = 1;
fp_write = fopen("test.txt", "w+");
fprintf(fp_write, "The int is %d\n", a);
fclose(fp_write);
}

that makes your code slightly easier to read - or you could simply close and then re-use the file handle :-

C++

main()
{
FILE *fp;
int t_size; 
 	
fp = fopen ("xxx.txt", "r"); 
fscanf(fp, "%d", &t_size); 
fclose(fp);

int a = 1;
fp = fopen("test.txt", "w+");
fprintf(fp, "The int is %d\n", a);
fclose(fp);
}

btw, no-where in your code do you show handling for end-of-file / error conditions

OriginalGriff · Accepted Answer · 2014-11-16T00:12:00

Easy! Just create a second FILE instance:

C++

FILE* fpInput;
FILE* fpOutput;

fpInput = fopen ("xxx.txt", "r"); 
fscanf(fpInput, "%d", &t_size); 

fpOutput = fopen ("yyy.txt", "w+"); 
fprintf(fpOutput, "The int is %d\n", t_size); 

fclose(fpInput);
fclose(fpOutput);

And please: it's considered rude to remove questions - it doesn't help others with a similar problem!

Compile 2 file commands in one in C

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