On 19.12.2022 11:32, Paul wrote:

> With C, there would be a temptation to write some
> low level text handlers, that a textual processor
> would already have. Maybe you can find a library for C
> to act as an assistant, so it's not an impossibility.

Just searched for a small C compiler which doesn't need
to be installed so you can store it on an USB stick and
use it on any computer.

https://download.savannah.gnu.org/releases/tinycc/
https://download.savannah.gnu.org/releases/tinycc/tcc-0.9.27-win32-bin.zip

Just put the content of the zip file in a new folder
and all you have to do is:

tcc your_program.c

It directly creates the binary your_program.exe

And here a small C program which inserts text after
a given number of lines in a file:

________________________________________________________

/* usage: ins infile outfile */
/* after line number LINE the text TEXT is inserted */

#define LINE 5
#define TEXT "user\npass\n"

/************************************************************************
external functions used: getc(); putc(); fopen(); fclose(); exit();
************************************************************************/

#include <stdio.h>
FILE *in, *out, *fopen();

void out_string();
void print_string();
void ende();
void exit();

main(nargs,args) int nargs; char *args[];
{if (nargs!=3) ende(1);
in = fopen(args[1],"rb"); if (in==NULL) ende(2);
out = fopen(args[2],"wb"); if (out==NULL) ende(3);

int i,n=0;
while ( (i=getc(in)) != EOF)
{putc(i,out);
if (i == 10) n++;
if (n == LINE) {n++; out_string(TEXT);}
}
ende(0);
}

void out_string(p) char *p; {while (*p) putc(*p++,out);}
void print_string(p) char *p; {while (*p) putc(*p++,stdout);}

void ende(i) int i;
{static char *(meld[]) = {
/* 0 */ "no errors" ,
/* 1 */ "usage: ins infile outfile" ,
/* 2 */ "can't open input file" ,
/* 3 */ "can't open output file" ,
/* 4 */ "you never should read this" ,
/* 5 */ "you never should read this" ,
/* 6 */ "you never should read this" ,
};

print_string("\n"); print_string(meld[i]); print_string("\n");
if (in!=NULL) fclose(in);
if (out!=NULL) fclose(out);
exit(0);
}