Question

hi every body
can some one help me with thi problem
i have a text file which is following

hi Hello this is my Hello to
 the Hello world

i write a code in c which is following

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

void main()
{
    FILE *fp,*fout;
    int i=0,len_string;
    char SearchText[]="Hello"; /* You can replace this text */
    char ReplaceText[]="Help"; /*You can also replace this text. */
    char temp[30];
    fp=fopen("ram.txt","a+");
    fout=fopen("temp.txt","a+");
    rewind(fp); /* for going to start of file. */
    if(fp==NULL || fout==NULL)
    {
        printf("File couldn't be opened ");
        exit(0);
    }
    len_string=strlen(SearchText);
    while(!feof(fp))
    {
        for(i=0;i<len_string;i++)
        { 
            temp[i]=fgetc(fp);
        }
        temp[i]='\0';
        if(strcmp(SearchText,temp)==0) /* the stricmp() is used for comparing both string. */
        {

            fprintf(fp,"%s ",ReplaceText);
            fprintf(fout,"%s",ReplaceText);
            fflush(fp);
            fclose(fp);
            fclose(fout);
            exit(1);
        }
    }
    fclose(fp);
    fclose(fout);
}

now my out put is like that

hi Hello this is my Hello to
 the Hello world

Help Help
what i m doing wrong ?
how to replace Hello to help in my text file ?
how to get my output like that?

hi Help this is my Hello to
 the Help world

can anybody explain with code ?

Answer 1

You are searching in 5-char groups for the string “Hello”. So you are looking at your file like this:

hi He
llo t
his i
s my 
Hello
 to\n 
the H
ello 
world

Only one of those matches what you are looking for. You should probably read the file line-by-line (using a larger buffer, just in case), and search/replace on each line for your search text.

Additionally, you are exiting 0 on failure and 1 on success (which is backwards; 0 means success, anything else means failure, traditionally). And you are exiting after the first match, rather than continuing onward looking for more.

To read line by line and perform search/replace, do something like this:

FILE *f = ...;
char buf[1024];
while (fgets(buf, sizeof(buf), f)) {
    char *pos;
    while ((pos = strstr(buf, search)) != NULL) {
        char temp = *pos;
        *pos = 0;
        fprintf(out, "%s%s", buf, replace);
        *pos = temp;
        buf = pos + strlen(search);
    }
    fprintf(out, "%s", buf);
}

This isn’t ideal, as a long line (> 1023 chars) will get cut into pieces, possibly in the middle of a search token, but it will work in most cases.