Search and replace char in same text file

[anii]

Hi there,

I've got this piece of code, but I'm having trouble getting it to write the changes into the file.

What I'm trying to do is:

• Read text file
• Find user specified character (eg. what to replace all the a's)
• Replace the character (eg. replace all a's with b's)
• Write to the same text file

#include <stdio.h>
#include <string.h>
 
#define MAX_LEN_SINGLE_LINE     1000
 
int main(int argc, char *argv[])
{
        if (argc < 4)
        {
                fprintf(stderr, "Format should be: %s  char to replace  char replacing\n", argv[0]);
                return 1;
        }
 
    char buffer[MAX_LEN_SINGLE_LINE+2];
    char *buff_ptr, *find_ptr, temp;
    FILE *fp1;
    size_t find_len = strlen(argv[2]);
 
    fp1 = fopen(argv[1],"r");
 
    while(fgets(buffer,MAX_LEN_SINGLE_LINE+2,fp1))
    {
        buff_ptr = buffer;
        while ((find_ptr = strstr(buff_ptr,argv[2])))
        {
            while(buff_ptr < find_ptr)
                fputc((int)*buff_ptr++,fp1);
 
            fputs(argv[3],fp1);
            buff_ptr += find_len;
        }
        fputs(buff_ptr,fp1);
    }
 
    fclose(fp1);
 
    return 0;
}
 

At the moment it compiles fine (with a few warnings) but when I check the file it does not have the changes made to it.

User would input something like: ./a.out myfile.txt a b
(that is - take myfile.txt - replace all a's and replace with b's)

Any help would be greatly appreciated!

[donbock]

On line 19 you open the file for reading ("r"). Try opening it for update ("r+"). Refer to the fopen man page for details.

[anii]

Hi donbock, thanks for your reply. I've changed the ("r") to ("r+") and tweeked the rest of the code to rewind and little and write.