Sponsored Content
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.
 

10 More Discussions You Might Find Interesting

1. AIX

Segmentation fault

I am tring to install Lotus Domino/Notes 5.0.5 on a AIX 4.3.3 server. I go to run the cdrom/ibmpow/install and I get the following error. Lotus Notes for Unix Install Program --------------------------------------------- ./install: 10088 Segmentation fault This had Lotus Notes installed... (1 Reply)
Discussion started by: jshaulis
1 Replies

2. Programming

Adding a single char to a char pointer.

Hello, I'm trying to write a method which will return the extension of a file given the file's name, e.g. test.txt should return txt. I'm using C so am limited to char pointers and arrays. Here is the code as I have it: char* getext(char *file) { char *extension; int i, j;... (5 Replies)
Discussion started by: pallak7
5 Replies

3. Programming

segmentation fault

If I do this. Assume struct life { char *nolife; } struct life **life; // malloc initialization & everything if(life->nolife == 0) Would I get error at life->nolife if it is equal to 0. wrong accession? (3 Replies)
Discussion started by: joey
3 Replies

4. 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)... (11 Replies)
Discussion started by: aaronwong
11 Replies

5. Programming

segmentation fault in fwrite function

Hi, my code is written in proC and it is in UNIX(AIX).I have written a small code for writing data into a binary file,but while writing my program is giving core dump. Here Is my code---- fpWriteFile = fopen(WriteFileName,"wb+"); CHAR *recvgen; recvgen = (char... (7 Replies)
Discussion started by: ajaysahoo
7 Replies

6. Programming

C++ segmentation fault while checking for null pointer

void disptree(node *ptr) { if ((ptr->left) !=NULL) disptree(ptr->left); cout<<"Position:"<<ptr->pos<<" Data:"<<ptr->data<<endl; if ((ptr->right)!=NULL; disptree(ptr->right); } i'm getting a segmentation fault at the red line. i cannot understand what's the problem.... (3 Replies)
Discussion started by: vijaymrt
3 Replies

7. Programming

segmentation fault while returning from function.

I am working on the application in which I have to fetch values from the database and paste in url and send it to portal. table=get_result("SELECT serialno,cas,Mode,FLC,TLC,location,CompName,CompCode,FG,FC,DispNo,TruckNo,LWbill,RRGPN,INVNO,DCN,RQTY,DQTY,SQTY,DDATE,RDATE,SDATE,TTIME FROM... (1 Reply)
Discussion started by: er.rohan88
1 Replies

8. Programming

Using gdb, ignore beginning segmentation fault until reproduce environment segmentation fault

I use a binary name (ie polo) it gets some parameter , so for debugging normally i do this : i wrote script for watchdog my app (polo) and check every second if it's not running then start it , the problem is , if my app , remain in state of segmentation fault for a while (ie 15 ... (6 Replies)
Discussion started by: pooyair
6 Replies

9. Shell Programming and Scripting

Segmentation fault in function call, shell script

I am getting Segmentation fault at below function call in my script: get_x() { sqlplus -s / <<end | grep KEEP | sed 's/KEEP//;s///g' select 'KEEP' ,table_name from all_synonyms where upper(synonym_name)= '$1'; exit end x=$(get_x $1) echo " SQL OUTPUT IS :: $x" } I am getting output of... (1 Reply)
Discussion started by: IB_88
1 Replies

10. Programming

C. To segmentation fault or not to segmentation fault, that is the question.

Oddities with gcc, 2.95.3 for the AMIGA and 4.2.1 for MY current OSX 10.14.1... I am creating a basic calculator for the AMIGA ADE *NIX emulator in C as it does not have one. Below are two very condensed snippets of which I have added the results inside the each code section. IMPORTANT!... (11 Replies)
Discussion started by: wisecracker
11 Replies
cdbmake(1)						      General Commands Manual							cdbmake(1)

NAME
cdbmake - create a constant database SYNOPSIS
cdbmake cdb cdb.tmp DESCRIPTION
cdbmake reads a series of encoded records from its standard input and writes a constant database to cdb. cdbmake ensures that cdb is updated atomically, so programs reading cdb never have to wait for cdbmake to finish. It does this by first writing the database to cdb.tmp and then moving cdb.tmp on top of cdb. If cdb.tmp already exists, it is destroyed. The directories con- taining cdb.tmp and cdb must be writable to cdbmake; they must also be on the same filesystem. cdbmake always makes sure that cdb.tmp is safely written to disk before it replaces cdb. If the input is in a bad format or if cdbmake has any trouble writing cdb.tmp to disk, cdbmake complains and leaves cdb alone. RECORD FORMAT Records are indexed by keys. A key is a string. cdb is structured so that another program, starting from a key, can quickly find the rel- evant record. cdbmake allows several records with the same key, although most readers take only the first record, and cdbmake slows down somewhat if there are many records with the same key. cdbmake and cdbdump(1) preserve the order of records. A record is encoded for cdbmake as +klen,dlen:key->data followed by a newline. Here klen is the number of bytes in key and dlen is the number of bytes in data. The end of data is indicated by an extra newline. For example: +3,5:one->Hello +3,7:two->Goodbye key and data may contain any characters, including colons, dashes, newlines, and nulls. Keys and data do not have to fit into memory. A database cannot exceed 4 gigabytes. cdb is portable across machines. SEE ALSO
cdbdump(1), cdbget(1), cdbstats(1) cdbmake(1)
All times are GMT -4. The time now is 08:39 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy