C - how to delete string the same string as user input from a file in c?

Question

I want to make a program that delete a String that the same as user input from a file below are contents in the file

G12
G13
G14

For example user input G13 , expected output is as following :

G12
G14

I got some idea that make a temporary file , but don't get any idea on how to get a string line by line because i print the file content using these code

if(file!=NULL)
{
    while ((c = getc(file)) != EOF)
    putchar(c);
    fclose(file);
}

so basically i reads all the file content only letter by letter (dont have any idea how to make it reads word by word

Thanks in advance

See also e.g. stackoverflow.com/questions/3501338/c-read-file-line-by-line — user707650
– user707650, Commented Apr 25, 2014 at 15:22
@gio : you cannot delete a line from a file, you must copy the whole file line by line omitting the line(s) you want to delete. — Jabberwocky
– Jabberwocky, Commented Apr 25, 2014 at 15:27
@MichaelWalz yes thats what i meant , so it means make a new temporary file and rename it to the original file , isnt it ? — Gio
– Gio, Commented Apr 25, 2014 at 15:31

BLUEPIXY · Accepted Answer · 2014-04-26 07:58:10Z

1

simple line by line sample

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

char *esc_cnv(char *str){
    char *in, *out;
    out = in = str;
    while(*in){
        if(*in == '\\' && in[1] == 'n'){
            *out++ = '\n';
            in += 2;
        } else 
            *out++ = *in++;
    }
    *out = '\0';
    return str;
}

int main(void){
    FILE *fin = stdin, *fout = stdout;
    char line[1024];
    char del_str[1024];
    char *p, *s;
    int len;
    int find=0;//this flag indicating whether or not there is a string that you specify 

    fin = fopen("input.txt", "r");
    fout = fopen("output.txt", "w");//temp file ->(delete input file) -> rename temp file.
    printf("input delete string :");
    scanf("%1023[^\n]", del_str);
    esc_cnv(del_str);//"\\n" -> "\n"
    len = strlen(del_str);
    while(fgets(line, sizeof(line), fin)){
        s = line;
        while(p = strstr(s, del_str)){
            find = 1;//find it!
            *p = '\0';
            fprintf(fout, "%s", s);
            s += len;
        }
        fprintf(fout, "%s", s);
    }
    fclose(fout);
    fclose(fin);
    if(find==0)
        fprintf(stderr, "%s is not in the file\n", del_str); 
    return 0;
}

edited Apr 26, 2014 at 7:58

answered Apr 25, 2014 at 21:19

BLUEPIXY

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6 Comments

Gio Over a year ago

could you please explain how does the 1st while and 2nd while work ? i cant get it at all , but ur code is working . Thanks before

Gio Over a year ago

and i am also wondering how to make an alert if the user input is not exist in the file ?

BLUEPIXY Over a year ago

@Gio 1st while : Repeat to read line by line from the file. 2nd while : Is repeated between string you want to delete exists.

BLUEPIXY Over a year ago

@Gio File is simply copied if the string to be deleted does not exist. Is switched to the process of simply deleting the temporal file by checking that there was no change of the flag when it has finished reading the file by using a flag to record that it has entered the inner loop.

Gio Over a year ago

i managed to make an Error message once the string that user input does not exist in the file , how do i get it ?

|

divivoma · Accepted Answer · 2014-04-25 16:28:53Z

0

Exactly as Micheal said. On a file you can do only write and read operation. So you must read the char and when you find the exact word that you don't want to write, just don't write it. Otherwise you write it :)

answered Apr 25, 2014 at 16:28

divivoma

134 bronze badges

2 Comments

Gio Over a year ago

read the char ? i wont work because michael said that i should compare the string ,

divivoma Over a year ago

A string is composed by multiple char. You should decide how to do the compare action. You can do it char by char or char[10] x char[10] using e.g. the strcmp function.

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