C-Stream

# help

man -S3 getopt

https://www.coursera.org/learn/interacting-system-managing-memory/supplement/IP2c9/complex-option-processing

Opening a File

Mode	Read and/or write	Does not exist?	Truncate?	Position
r	read only	fails	no	beginning
r+	read/write	fails	no	beginning
w	write only	created	yes	beginning
w+	read/write	created	yes	beginning
a	writing	created	no	end
a+	read/write	created	no	end

https://www.coursera.org/learn/interacting-system-managing-memory/supplement/Aj8DG/opening-a-file

read file

#include <stdio.h>
#include <string.h>
int main(int argc, char ** argv){
 if (argc !=2) {
   printf("arg error");
 }
 FILE * f  = fopen(argv[1],"r");
 if (f==NULL) {
  printf("file open failed");
 }
 int c;

 while ((c=fgetc(f))!=EOF) {
  printf("%c",c);  
 }
}

output

fjeijfi jfief

./file test.txt

fgets

#include <stdlib.h>
# define LINE_SIZE 5

#include <stdio.h>
#include <string.h>
int main(int argc, char ** argv){
    if (argc !=2) {
        printf("arg error");
    }
    FILE * f  = fopen(argv[1],"r");
    if (f==NULL) {
        printf("file open failed");
    }
    int c;

    long total = 0;
    char line[LINE_SIZE];
    while (fgets(line,LINE_SIZE,f)!=NULL) {
        if (strchr(line,'\n')==NULL) {
            printf("Line is too long!\n");
            return EXIT_FAILURE;
        }
        total += atoi(line);
    }
    printf("The total is %ld\n",total);
    return  EXIT_SUCCESS; 
}

./fgets num.txt

output : Line is too long!

å

123

14

-56789

77

Writing to Files

You can also use fputc to write a single character at a time, or fputs to write a string without any format conversions. That is, if you do fputs(“%d”) it will just print “%d”to the file directly rather than attempting to convert an integer and print the result.

C library functions may buffer the data, and not immediately request that the OS write it. Even once the application makes the requisite system calls to write the data, the OS may buffer it internally for a while before actually writing it out to the underlying hardware device.

https://www.coursera.org/learn/interacting-system-managing-memory/supplement/OFKPW/writing-to-files

Closing Files

We will not concern ourselves with complex corrective actions when fclose fails—printing an error message suffices. However, you should get in the habit of checking its return value. This way, when you are working on real programs, you will check the return value by habit, and at least think about what you should do if it fails.

https://www.coursera.org/learn/interacting-system-managing-memory/supplement/DveF8/closing-files