Need to replace some text after ":" in c

thurst1 · 07-16-2014, 07:16 AM

I have a file with contents like below, need to replace the last set "zzzz" in every line with 0.

I tried using strtok, strstr for this this purpose but not getting desired results.

<file contents>
xxxx:yyyy:zzzz
....:....:....
....:....:....
....:....:....

metcommradio · 07-16-2014, 07:36 AM

Not sure what you mean really but keeping things simple, you might try to read the file (or paste the text content) into your favourite text editor and use the 'Search & Replace' function ... ? I spent ages once trying to achieve a similar issue in a spreadsheet only to later realise that this simple solution was easier.

Sorry if I'm on the wrong track ....

turtleli · 07-16-2014, 07:53 AM

Did you try using strrchr?

thurst1 · 07-16-2014, 08:06 AM

Quote:

Originally Posted by metcommradio

Not sure what you mean really but keeping things simple, you might try to read the file (or paste the text content) into your favourite text editor and use the 'Search & Replace' function ... ? I spent ages once trying to achieve a similar issue in a spreadsheet only to later realise that this simple solution was easier.

Sorry if I'm on the wrong track ....

I am trying this c program.

thurst1 · 07-16-2014, 08:36 AM

Quote:

Originally Posted by turtleli

Did you try using strrchr?

No, Can you help on this?

schneidz · 07-16-2014, 08:39 AM

maybe reverse the string (strrev()) then read up to the first: then truncate and replace ?

strrchr() implicitly reverses then searches in one function:
http://linux.die.net/man/3/strrchr

NevemTeve · 07-16-2014, 09:12 AM

> No, Can you help on this?

It should be quite easy:

Code:

    ...
    while (fgets (line_buffer, sizeof (line_buffer), input_file)) {
        char *lastcolon= strrchr (line_buffer, ':');
        if (lastcolon) {
            /* do some transformation */
        }
        fputs (line_buffer, output_file);
    }

mina86 · 07-17-2014, 08:44 AM

When using fgets don't forget to check whether you've read the whole line. Also be sure to not go over the buffer in “do some transformation”.

rtmistler · 07-17-2014, 01:59 PM

If every line in your file follows a consistent format, you can perform sscanf() on the input line.

Code:

int ret;

if((ret = sscanf(input_buffer, "%s:%s:%s:")) != 3) {
    printf("Error: did not find correct format, ret=%d on line %s\n", ret, input_buffer);
}

Plus, make a test program, turn off optimization, enable GDB debugging when you compile, save returns and information as much as possible in variables, and use GDB to debug the process line by line.

thurst1 · 07-18-2014, 09:17 AM

Quote:

Originally Posted by rtmistler

If every line in your file follows a consistent format, you can perform sscanf() on the input line.

Code:

int ret;

if((ret = sscanf(input_buffer, "%s:%s:%s:")) != 3) {
    printf("Error: did not find correct format, ret=%d on line %s\n", ret, input_buffer);
}

Plus, make a test program, turn off optimization, enable GDB debugging when you compile, save returns and information as much as possible in variables, and use GDB to debug the process line by line.

Hi,
My file has only one line so i am thinking of using fscanf to parse the lines.
i am using fscanf(fp,"%s %d", str,&num). But if my file has something like "abcd 1234". It is not working , how to configure format specifier for this scenario?

NevemTeve · 07-18-2014, 09:25 AM

> My file has only one line so i am thinking of using fscanf to parse the lines.

One line? Did you count carefully enough?

rtmistler · 07-18-2014, 09:32 AM

This example works fine:

Code:

#include <stdio.h>

void main(void)
{
    FILE *fptr;
    int ret;
    char input[32];
    int value;

    if((fptr = fopen("data.txt", "r")) == NULL) {
        printf("Unable to open data.txt file, exiting.\n");
        return;
    }

    if((ret = fscanf(fptr, "%s %d", input, &value)) != 2) {
        printf("fscanf returned %d\n", ret);
    }
    else {
        printf("Scanned string: %s\n", input);
        printf("Scanned number: %d\n", value);
    }
}

Contents of data.txt:

Code:

abcde 012345

Sample output:

Code:

Scanned string: abcde
Scanned number: 12345

thurst1 · 07-18-2014, 09:40 AM

Quote:

Originally Posted by rtmistler

This example works fine:

Code:

#include <stdio.h>

void main(void)
{
    FILE *fptr;
    int ret;
    char input[32];
    int value;

    if((fptr = fopen("data.txt", "r")) == NULL) {
        printf("Unable to open data.txt file, exiting.\n");
        return;
    }

    if((ret = fscanf(fptr, "%s %d", input, &value)) != 2) {
        printf("fscanf returned %d\n", ret);
    }
    else {
        printf("Scanned string: %s\n", input);
        printf("Scanned number: %d\n", value);
    }
}

Contents of data.txt:

Code:

abcde 012345

Sample output:

Code:

Scanned string: abcde
Scanned number: 12345

Can we replace the the number with "0" and save in the same file?

rtmistler · 07-18-2014, 10:00 AM

Not sure what you're asking. I realize that I did overlook the fact that scanning "012345" as an integer would result in 12345. This does work if the line of data is "abcd 1234" and gives you "abcd" as a string and 1234 as a number.

Copy that code, compile it, and test it for yourself.

If you're saying that you'd like to write that data out to a file. I'd recommend you write it to a different file, for starters. Because opening a file in append mode versus create-read/write mode have different behaviors insofar as what does or doesn't happen to the existing file contents as well as where the read and write pointers start out at.

But if you just fopen() a different file with "w" then it will always create a new file and start writing at the top of that new file. It will also always overwrite any same named file.

I suggest that you should develop an understanding about reading and writing separately first before you play with modifying in place.

smeezekitty · 07-25-2014, 01:38 PM

You might make use of mmap() to map a file to memory which makes editing in place quite easy