segfault in pointer to string program Post: 302556107

Sponsored Content

Top Forums Programming segfault in pointer to string program Post 302556107 by Corona688 on Friday 16th of September 2011 02:59:51 PM

09-16-2011

Registered User

Quote:

Originally Posted by zius_oram

got it

thank you so much. do C through segfault for any particular type of error?? i wanna know when exactly C throws segfault?

All 'segfault' means is that your program attempted to access a memory page that either
1) doesn't exist, or
2) your program doesn't have permissions to access.

There's almost endless reasons why a program could end up doing that but it's often a logic error of some sort -- not checking the return value of something and dereferencing a NULL, going beyond array bounds and accidentally overwriting nearby variables, reusing a pointer you already free()'d and mangling whatever data(if anything) ended up in it later... You can even corrupt the stack frame itself so return jumps the program to invalid memory and bombs out long after the actual error was made. And lots more.

You went beyond array bounds, which would have started modifying the values of local stack variables. This can go wrong in many interesting ways... it could have kept going until you'd mangled your entire stack and hit the bottom of memory. Or (more likely) when you started mangling local stack variables, the value of s was set to some bizzare value which pointed to invalid memory.

Last edited by Corona688; 09-16-2011 at 04:04 PM..

This User Gave Thanks to Corona688 For This Post:

Corona688

View Public Profile for Corona688

Visit Corona688's homepage!

Find all posts by Corona688

10 More Discussions You Might Find Interesting

1. Programming

String and pointer problem

i am having a string like " X1 " ---> string lenght is 30 I have stored this to a chararry . ref so here ref = " X1 " now i trim the left space by my function . Si the string now becomes "X1 " ---> string lenght is 15...

2. Programming

pass a pointer-to-pointer, or return a pointer?

If one wants to get a start address of a array or a string or a block of memory via a function, there are at least two methods to achieve it: (1) one is to pass a pointer-to-pointer parameter, like: int my_malloc(int size, char **pmem) { *pmem=(char *)malloc(size); if(*pmem==NULL)...

3. Programming

id3lib SEGFAULT

Hello everyone, I'm writing a program using the id3lib unfortunately I've encountered with memory issue that cause segmentation fault. I tried to rerun and analyze the program with valgrind but it doesn't point me anywhere. I really stuck on this one. Valgrind output: ==14716== Invalid read of...

4. Programming

C++ program is crashing on re-assigning const static member variable using an int pointer

Hi, Can any one tell me why my following program is crashing? #include <iostream> using namespace std; class CA { public: const static int i; }; const int CA::i = 10; int main() { int* pi = const_cast<int*>(&CA::i); *pi = 9; cout << CA::i << endl; }

5. UNIX for Dummies Questions & Answers

Counting vowels in string. "Comparison pointer-integer".

I'm trying to write a programme which scans strings to find how many vowels they contain. I get an error saying that I'm trying to compare a pointer and an integer inif(*v == scanme){. How can I overcome this ? Also, the programme seems to scan only the first word of a string e.g.: if I type "abc...

6. Programming

How i use pointer as a string in c programing?

I'm newbie learner. My all friend use windows just only me use linux. so i can't solve any problem by myself. i need a solution. how can i use pointer as a string. #include<string.h> #include<stdio.h> int main() { char *s='\0'; gets(s); puts(s); return 0; } This code work on...

7. Programming

String array iteration causing segfault

I am populating an array of string and print it. But it going in infinite loop and causing segfault. char Name = { "yahoo", "rediff", "facebook", NULL }; main(int argc, char* argv) { int j = 0; ...

8. Programming

Scanf() string pointer problem

I have a problem with scanf() for string pointer as member of a struct. #include <stdio.h> #include <stdlib.h> struct Student { int studentNumber; int phoneNumber; char *studentName; //line 7 // char studentName; //line 8 }; int...

9. Programming

String pointer does not work

Hello, I am trying to reverse complement one string and reverse another (NO complement!), both with pointer. My code compiled without error, but did not do the job I wanted. #include <stdio.h> #include <stdlib.h> #include <zlib.h> #include "kseq.h" // STEP 1: declare the type of file...

10. Programming

Segfault When Parsing Delimiters In C

Another project, another bump in the road and another chance to learn. I've been trying to open gzipped files and parse data from them and hit a snag. I have data in gzips with a place followed by an ip or ip range sort of like this: Some place:x.x.x.x-x.x.x.x I was able to modify some code...

LEARN ABOUT NETBSD

stack

STACK(9)						   BSD Kernel Developer's Manual						  STACK(9)

NAME

     STACK -- stack macros

SYNOPSIS

     #include <sys/param.h>

     type
     STACK_ALLOC(sp, size);

     type
     STACK_MAX(sp, size);

     type
     STACK_ALIGN(sp, bytes);

     type
     STACK_GROW(sp, size);

     type
     STACK_SHRINK(sp, size);

DESCRIPTION

     A stack is an area of memory with a fixed origin but with a variable size.  A stack pointer points to the most recently referenced location
     on the stack.  Initially, when the stack has a size of zero, the stack pointer points to the origin of the stack.	When data items are added
     to the stack, the stack pointer moves away from the origin.

     The STACK_ALLOC() macro returns a pointer to allocated stack space of some size.  Given the returned pointer sp and size, STACK_MAX() returns
     the maximum stack address of the allocated stack space.  The STACK_ALIGN() macro can be used to align the stack pointer sp by the specified
     amount of bytes.

     Two basic operations are common to all stacks: a data item is added (``push'') to the location pointed by sp or a data item is removed
     (``pop'') from the stack.	The stack pointer must be subsequently adjusted by the size of the data item.  The STACK_GROW() and STACK_SHRINK()
     macros adjust the stack pointer sp by given size.

     A stack may grow either up or down.  The described macros take this into account by using the __MACHINE_STACK_GROWS_UP preprocessor define.

SEE ALSO

     param(3), queue(3)

BSD
								   April 8, 2011							       BSD