How to add text at the end of line - c

Question

for example I have test.txt with
test1
test2
at the end of each line I would like to add some text
my code is:
fp = fopen("test.txt", "w");
while ((ch=getc(fp)) != EOF)
if (ch == '\n')
fprintf(fp, "newText");
my output is:
test1
newText
The outcome should be:
test1newText
test2newText

Answer 1

You cannot do it with a single file.
Here is what you need to do:
Open an auxiliary file for temporary output
Read the actual file line by line
For each line write the copy of the line into the auxiliary output
After writing the line write the suffix that you would like to append
Go to the next line until you process the whole file
Once you finished processing the whole file, close both files, and move the auxiliary file in place of the original input.
How to avoid a new line?, I successfully copy [the text] but when I try to add some text at the end of each line, it starts from new line
This is because you include the end-of-line character in your copied text.
If you read character-by-character, do not copy '\n's when you see them; if you read with fgets, check the last character, and skip it if it happens to be '\n' (fgets includes it in its return value).

Answer 2

You can’t read from your output file like that. It is possible to open a file for reading and writing, but it’s an advanced topic and isn’t really appropriate for text files.
The normal approach is to write to another file, and then replace the original if desired. Note that you’ll have to emit all the characters you read and your extra text.
If this is the whole function of the program, consider making it a filter (by using the standard streams); this is what’s expected by experienced users and saves some error checking.

Answer 3

eventually, I have succeed
if (!strcmp(fileName, SWM_DEBUG))
{
fp = fopen(fileName, "r");
fpOut = fopen("tmp.txt", "w");
while ((ch = fgetc(fp)) != EOF)
{
if (ch == '\n')
fprintf(fpOut, "TEST");
fputc(ch, fpOut);
}
}
Thanks for your support ☺

Answer 4

You need to change the fopen call to read from the file and use the fputc function to re-output the character you read, like this:
fp = fopen("test.txt", "r");
while ((ch=fgetc(stdin)) != EOF) {
if (ch == '\n') {
fprintf(fp, "newText");
}
fputc(ch, fp);
}
fprintf(fp, "newText");
As pointed out elsewhere, you can't simultaneously read and write a file in the way you were trying to do, so i've changed it to read from stdin to illustrate the code