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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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DH_MOVEFILES(1) 						     Debhelper							   DH_MOVEFILES(1)

NAME
dh_movefiles - move files out of debian/tmp into subpackages SYNOPSIS
dh_movefiles [debhelperoptions] [--sourcedir=dir] [-Xitem] [file...] DESCRIPTION
dh_movefiles is a debhelper program that is responsible for moving files out of debian/tmp or some other directory and into other package build directories. This may be useful if your package has a Makefile that installs everything into debian/tmp, and you need to break that up into subpackages. Note: dh_install is a much better program, and you are recommended to use it instead of dh_movefiles. FILES
debian/package.files Lists the files to be moved into a package, separated by whitespace. The filenames listed should be relative to debian/tmp/. You can also list directory names, and the whole directory will be moved. OPTIONS
--sourcedir=dir Instead of moving files out of debian/tmp (the default), this option makes it move files out of some other directory. Since the entire contents of the sourcedir is moved, specifying something like --sourcedir=/ is very unsafe, so to prevent mistakes, the sourcedir must be a relative filename; it cannot begin with a `/'. -Xitem, --exclude=item Exclude files that contain item anywhere in their filename from being installed. file ... Lists files to move. The filenames listed should be relative to debian/tmp/. You can also list directory names, and the whole directory will be moved. It is an error to list files here unless you use -p, -i, or -a to tell dh_movefiles which subpackage to put them in. NOTES
Note that files are always moved out of debian/tmp by default (even if you have instructed debhelper to use a compatibility level higher than one, which does not otherwise use debian/tmp for anything at all). The idea behind this is that the package that is being built can be told to install into debian/tmp, and then files can be moved by dh_movefiles from that directory. Any files or directories that remain are ignored, and get deleted by dh_clean later. SEE ALSO
debhelper(7) This program is a part of debhelper. AUTHOR
Joey Hess <joeyh@debian.org> 11.1.6ubuntu2 2018-05-10 DH_MOVEFILES(1)
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