Replacing a word in a file, using C

Question

How do I replace a word in a file with another word using C?

For example, I have a file which contains:

my friend name is sajid

I want to replace the word friend with grandfather, such that the file is changed to:

my grandfather name is sajid

(I am developing on Ubuntu Linux.)

Update:

I am doing filing in C. I have created a .txt file and write some data into it, but as my program progresses I have to search some text and replace it with the other words. The problem I am facing is that suppose in my file I wrote

"I bought apple from the market"

If i replace apple with pineapples as apple has 5 char and pineapple has 9 char it will write it as

"I bought pineapple m the market"

It also has affected the words written after apple.

I have to do it using C, not a command line script.

You have to learn how to ask questions first. I bet that if you rephrase, and clearly state your problem, you will find a solution yourself. See http://www.catb.org/~esr/faqs/smart-questions.html — , Feb 18 '11 at 14:12
Im a bit confused at what your asking? Or what language/program your using? Since most text editors have a Replace Function? — , Feb 18 '11 at 14:15
Similar questions : http://stackoverflow.com/questions/2672581/string-replace-in-file-using-c and http://stackoverflow.com/questions/1733058/replace-placeholders-with-text-c and http://stackoverflow.com/questions/2211749/c-file-programming-replace-a-text-in-a-file-using-posix-calls — Shawn Chin, Feb 18 '11 at 14:30
Hi mainajaved, have you solved the problem? I have the same problem as you. It will be nice if you could share the solution here. — Sakura, Jun 18 '13 at 08:01

score 1 · Answer 1 · edited May 23 '17 at 12:04

1

How about using the exiting Linux sed program?

sed -i 's/friend/grandfather/' filename

That will replace friend with grandfather in the existing file. Make a copy first if you want to keep the original!

Edit:

Alternatively, load the file into an STL string, replace 'friend' with 'grandfather' using a technique such as this, and save the new string into a file.

edited May 23 '17 at 12:04

Community

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answered Feb 18 '11 at 14:09

Kernow Steve

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He did mention that he wanted to do it in `C`. – Shawn Chin Feb 18 '11 at 14:10
I know, but using sed would save him having to code anything. It isn't clear if sajid _has_ to write the code, or is writing the code just to do search/replace on the file. – Kernow Steve Feb 18 '11 at 14:12
1

It sounds like a task which one would do to learn `C` (or perhaps homework?). Using `sed` wouldn't be of much benefit if that's the case. – Shawn Chin Feb 18 '11 at 14:17
True. Would spawning sed from C be classed as cheating? ;) – Kernow Steve Feb 18 '11 at 14:19
I believe it would be! Nice try... :) – Shawn Chin Feb 18 '11 at 14:21

score 1 · Answer 2 · answered Feb 18 '11 at 15:17

As you've realized, you won't be able to make the change in place in the original file.

The easy solution is to read each string from the original file and write it to standard output, making the replacement as necessary. In pseudocode:

open original file
while not at end of original file
  get next string from original file
  if string == "friend"
    write "grandfather" to standard output
  else
    write string to standard output
end while

You can then redirect the output to another file when you execute it, similar to how sed and awk work.

Alternately, you can create a destination file in the code and write to it directly. If you need to replace the original file with the new file, you can use the remove() and rename() library functions in stdio.

thanks so much John Bode got your point but also i have one other problem that continously updating and every line of file has differnt word to replace with i you want i will explain you my program — mainajaved, Feb 18 '11 at 15:31

Replacing a word in a file, using C

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