Thread: Mysterious fprintf problem

I have experienced some mysterious problems when trying to write something into a file.

The output file is created by fopen in the beginning of the program. The idea is at the end of the run I want to write some data into the file, using fprintf.

1 If I write something (e.g. "Hello world \n") into the output file at the beginning of my program, everything is fine. At the end of the program the data I really want is written into the output file (after the "Hello world\n" statement).

2 If I don't write any statement at the beginning of the run, the progran crashes when it is time to write data into the file. A segmentation fault message is generated, and the output file remains empty.

Can anyone explain such mysterious behavior?

Thanks,

Tor

Post your source code also.

Or atleast the part that is relavent to your problem.

Other's can't just guess your code and reply.

OK, in the beginning of main we have

FILE *infile, *outfile;

main(int argc, char *argv[])
{
outfile = fopen(argv[2], "w");

fprintf(outfile, "Hello world\n");

8<---------------------------
Big fat program that never calls outfile with fprintf or anything else. At the end of main, the function report is called.
8<---------------------


void report(void)
{
/* Compute and write estimates of desired measures of performance. */

printf("Before fprintf\n");

fprintf(outfile, "Simulation results: \n\n");
8<----------------------------

Observations:

1 the program works when the "Hello world" clause is there (except for the annoying greeting at the beginning of the data file).

2 When "Hello world" is removed, the program crashed at "Simulation results:". It says Segmentation fault. I know that it crashes at that statment because I have used printf command such as the one shown to determine exactly where it goes wrong.

Let me know if anybody has a clue. I am using a Sun workstation if it helps.

Best,

Tor

By moving around the "Hello world" statement I have moved closer to a resolution.

The program consists of several separately compiled .o but linked .o files.


OK:
outfile = fopen("Data.out", "w");
fprintf(outfile, "Hello world\n");
function_that_lives_in_different_object();

Also OK:
outfile = fopen("Data.out", "w");
fprintf(outfile, "Hello world\n");
function_that_lives_in_different_object();
fprintf(outfile, "Hello world again\n");

Not OK (Segmentation fault)
outfile = fopen("Data.out", "w");
function_that_lives_in_different_object();
fprintf(outfile, "Hello world\n");

It seems like the data.out file has to be accessed at least once before I start calling other objects. Can anybody explain why this would be...?

Tor

Just curious what this function_that_lives_in_different_object();
do?

For the two of you, try not creating a global FILE pointer. Create it in main, open it in main, and pass it to the other functions.

Code:

//prototype for report function.
void report(FILE *);

//call report like this.
report(outfile);

//receive the file pointer like this in the report function.
void report(FILE *outfile2)

Also in the code, I don't see you close the files, with fclose().

arsh, forgot myself to close. hope my system closed it!