Segmentation fault (core dumped) in c using linux – special case

I am basically trying to create a log file which has date and time as its name. This is my code

     char logger [500];

     time_t time1;
     struct tm * timeinfo; 
     time (&time1);
     timeinfo = localtime (&time1);
     sprintf(logger, "TestTreiber_%d%d%d%d%d%d.log",timeinfo->tm_year+1900,timeinfo->tm_mon+1,timeinfo->tm_mday,timeinfo->tm_hour,timeinfo->tm_min,timeinfo->tm_sec);

     printf("All logging during this test is done in : %s",logger);

     sprintf(logger, "prot/%s",logger);//STEP 1: I encounter the error here

     FILE *logFile;
     logFile= fopen(logger,"w");

Without the step 1 every thing worked fine. It created a log file with the name I wanted in the same folder where my program is. But when I add step 1 into the mix it gives me this error.

Segmentation Fault (core dumped)

I am new to Linux but I know it has something to do with memory so I increased the memory allocated to logger[500] (it was earlier 255 which worked fine). But I can’t seem to solve this problem. prot folder does exist in the directory I am running this. Please help!

PS Sorry about wrong usage of capital letters, I am using a German Keyboard.

Answer

You should not do this in your code,

sprintf(logger, "prot/%s",logger);

Quoting from the man page of sprintf,

Some programs imprudently rely on code such as the following,

sprintf(buf, "%s some further text", buf);

to append text to buf. However, the standards explicitly note that the results are undefined if source and destination buffers overlap when calling sprintf(), snprintf(), vsprintf(), and vsnprintf(). Depending on the version of gcc used, and the compiler options employed, calls such as the above will not produce the expected results.