C programming, fprintf() not working correctly

Question

Probably a silly mistake I am doing here.

    FILE *fp;
    fp = fopen("test.txt", "a+");
    fprintf(fp, time_stamp(),"FLAG 1, Timestamp : %s\n");
    fclose(fp);

I am getting timestamp from a function But The file writing only timestamp, not the flag If I remove timestamp, FLAG 1 printing. But Not getting together. ie

Flag 1, Timestamp : 20141005141116

The output I am getting in test.txt like

20141005145640201410051456402014100514564020141005145640201410051456412014100514564120141

Not going to new line and print like:

Flag 1, Timestamp : 20141005141116
Flag 1, Timestamp : 20141005141117
Flag 1, Timestamp : 20141005141118

..... like that

Please solve this issue

Please compile with all warnings & debug info (gcc -Wall -Wextra -g). You would get a warning from the compiler, if using GCC... — Basile Starynkevitch
– Basile Starynkevitch, Commented Nov 5, 2014 at 9:42

unwind · Accepted Answer · 2014-11-05 10:58:19Z

8

You have the arguments to fprintf() in the wrong order. Look at the manual page's prototype:

int fprintf(FILE *stream, const char *format, ...);

Clearly, the formatting string comes before the things being formatted (the variable part ...).

Assuming time_stamp() returns a static string, your code should be:

fprintf(fp, "FLAG 1, Timestamp : %s\n", time_stamp());

edited Nov 5, 2014 at 10:58

answered Nov 5, 2014 at 9:38

unwind

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5 Comments

ninja.stop Over a year ago

fprintf("FLAG 1, Timestamp : %s\n",fp,timestamp()); Is that? actually doing c after a long time hence...basic problems

unwind Over a year ago

@anupam_on Uh no? Please look at the prototype, or the code I gave you in the answer above. First the file pointer, then the formatting string, then the things being formatted.

Sarima Over a year ago

+1. This is possibly the nicest answer I have ever seen. Concise, to the point and all the relevant links.

unwind Over a year ago

@Joshpbarron Gee, thanks! I try, and in this regard I think practice really helps. :)

ninja.stop Over a year ago

Joshpbarron ya, correctly said, very rare type of answering. But yes, some people are there to do things precisely, to the point and correctly :) Thanks buddy @unwind Problem solved :)

Sourav Ghosh · Accepted Answer · 2014-11-05 09:57:57Z

3

Arguments to fprintf() should be like this :

fprintf(fp, "FLAG 1, Timestamp : %s\n", time_stamp());

edited Nov 5, 2014 at 9:57

Sourav Ghosh

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answered Nov 5, 2014 at 9:41

Shwetha

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