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Top Forums Programming Segmentation fault when I pass a char pointer to a function in C. Post 303016197 by jose_spain on Saturday 21st of April 2018 10:16:06 AM
Old 04-21-2018
Thanks, but I want to understand pointers use and this is the reason that I do it with a pointer.

I have done new tests with this program and I have found that:

1) If tmp is declared and initialized in main so, it works right without changes in "reverse" function:

Code:
char* tmp;

  tmp = (char*) malloc ((strlen("hello") + 1) * sizeof(char));
  strcpy(tmp, "hello");
  printf("tmp=%s\n" , tmp);
  reverse(tmp);
  printf("After calling reverse: tmp=%s\n\n" , tmp);

The program prints:

Code:
tmp=hello
After calling reverse: tmp=olleh

2) If instead I do this:

Code:
char* tmp = "hello";

  printf("tmp=%s\n" , tmp);
  reverse(tmp);
  printf("After calling reverse: tmp=%s\n\n" , tmp);

Then I get the segmentation fault.

What is the difference?

In this second case, If I check the value of s in reverse, it is:
"hello" + 0 (end of string mark)


Moderator's Comments:
Mod Comment Seriously: Please use CODE tags as required by forum rules!

Last edited by RudiC; 04-21-2018 at 11:20 AM.. Reason: Added CODE tags.
 

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pfm_enable_faults(3ncs) 												   pfm_enable_faults(3ncs)

Name
       pfm_enable_faults - enable asynchronous faults

Syntax
       #include <idl/c/base.h>
       #include <idl/c/pfm.h>

       void pfm_$enable_faults()

Description
       The routine enables asynchronous faults after they have been inhibited by a call to causes the operating system to pass asynchronous faults
       on to the calling process.

       While faults are inhibited, the operating system holds at most one asynchronous fault.  Consequently, when returns, there can  be  at  most
       one  fault waiting on the process.  If more than one fault was received between routines to and the process receives the first asynchronous
       fault received while faults were inhibited.

Diagnostics
       This section lists the status codes for errors returned by this routine.

       pfm_$bad_rls_order  Attempted to release a clean-up handler out of order.

       pfm_$cleanup_not_found
			   There is no pending clean-up handler.

       pfm_$cleanup_set    A clean-up handler was established successfully.

       pfm_$cleanup_set_signalled
			   Attempted to use pfm_$cleanup_set as a signal.

       pfm_$invalid_cleanup_rec
			   Passed an invalid clean-up record to a routine.

       pfm_$no_space	   Cannot allocate storage for a clean-up handler.

Files
See Also
       intro(3ncs), pfm_enable(3ncs), pfm_inhibit_faults(3ncs)

															   pfm_enable_faults(3ncs)
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