Hello I have a project I'm doing and I need my program to run from the command line and be able to read flags and file names that will be used in the program.
This is my current code. It compiles without entering any flags. I don't think my GetArgs does anything. I had help with that part of the code.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 1024
#define IN 1 /* inside a word */
#define OUT 0 /* outside a word */
/* count lines, words, and characters in input */
int numInputArgs;
int idx;
void GetArgs (int argc, char **argv){
for (idx = 1; idx < 4; idx++) {
if (strcmp(argv[idx], "-c") == 0) {
printf("Flag -c passed\n");
break;
}
else if (strcmp(argv[idx], "-w") == 0) {
printf("Flag -w passed\n");
break;
}
else if (strcmp(argv[idx], "-l") == 0) {
printf("Flag -l passed\n");
break;
}
else if (strcmp(argv[idx], "-L") == 0) {
printf("Flag -L passed\n");
break;
}
else {
printf("Error: unknown flag\n");
exit(-1);
}
}
}// end GetArgs
void lineWordCount ( ) {
int c, nl, nw, nc, state;
state = OUT; nl = nw = nc = 0;
while ((c = getchar()) != EOF) {
++nc;
if (c == '\n')
++nl;
if (c == ' ' || c == '\n' || c == '\t')
state = OUT;
else if (state == OUT) {
state = IN; ++nw;
}
printf("%d %d %d\n", nl, nw, nc);
}
}// end lineWordCount
int main(int argc, char **argv){
GetArgs(argc, argv);
lineWordCount();
printf("Hello");
//fclose( src );
}
You can either use a standard function like getopt() as mentioned by #Joachim, if it is available on your system, or you can code it yourself. If you have a complicated command line syntax, getopt() might be better suited - if you only need to check for a limited set of flags, it might be easier to code it yourself, for example:
void GetArgs (int argc, char **argv){
int idx = 0;
for (idx = 1; idx < argc; idx++) {
if (strcmp(argv[idx], "-a") == 0) {
printf("Flag -a passed\n");
} else if (strcmp(argv[idx], "-b") == 0) {
printf("Flag -b passed\n");
} else if (strcmp(argv[idx], "-c") == 0) {
printf("Flag -c passed\n");
} else {
printf("Error: unknown flag %s\n");
}
}
}
I recommend you to use argtable2 library. I have used it for a long time and I think it is great. There are tutorials available to see how powerful and easy to use it is.
Related
I wrote a program that copies the standard entry into the stdout as well as into a file. The program works but I have a problem, I receive a warning when compiling with make:
warning: implicit declaration of function ‘isprint’ [-Wimplicit-function-declaration]
if (isprint(optopt))
^~~
code:
Although it's not a big deal, I'd like it to stop displaying this warning. What would be the problem? I would also like a review of the code, what could I improve?
The program behaves like the tee -a file command.
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
static int append_mode = 0;
int parse_args(int argc, char *argv[])
{
char c;
while ((c = getopt(argc, argv, "a")) != -1) {
switch (c) {
case 'a':
append_mode = 1;
break;
case '?':
if (isprint(optopt))
fprintf(stderr, "Unkonw option `-%c'.\n", optopt);
else
fprintf(stderr,
"Unknown option character `\\x%x'.\n", optopt);
return 1;
default:
abort();
break;
}
}
return 0;
}
int main(int argc, char *argv[])
{
char buf[100];
size_t len;
char *file_mode;
int i;
FILE *files[20];
int num_files;
if (parse_args(argc, argv)) {
return 1;
}
file_mode = (append_mode ? "a" : "w");
num_files = argc - optind;
if (num_files > 0) {
if (files == NULL) {
fprintf(stderr, "Unable to allocate file buffer space\n");
return 1;
}
/* go through file arguments and either open for writing
or append based on the -a flag */
for (i = optind; i < argc; i++) {
FILE *pFile = fopen(argv[i], file_mode);
if (pFile == NULL)
{
fprintf(stderr, "Unable to open file %s for mode %s",
argv[i], file_mode);
goto main_cleanup;
}
files[i - optind] = pFile; /* mind the offset */
}
}
FILE *not_stdin = fopen("tee.c", "r");
while ((len = fread(&buf[0], 1, sizeof(buf), not_stdin)) > 0) {
fwrite(&buf[0], 1, len, stdout);
for (i = 0; i < num_files; i++) {
fwrite(&buf[0], 1, len, files[i]);
}
}
main_cleanup:
if (num_files > 0) {
for (i = 0; i < num_files; i++) {
fclose(files[i]);
}
}
return 0;
}
Mostly this warning appears when you are trying to use a function without including its required header.
To use isprint() add #include <ctype.h> to your included headers.
i've created a program which is a re-make of the wc program in BASH. For some reason my check doesn't work as it should. Word count and Line count (which are handled by my child processes, using fork) still display when they should not. if i type './test -n' it is only meant to display the current user. however it seems to display that followed by word and line count, even though i didn't ask for it. the if statement which doesn't seem to work is near the bottom of the code. here is my code:
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <sys/wait.h>
/* Size of character buffer to read in a file. */
#define BUFFSIZE 1000000
/* Read file 'filename' into character buffer 'text'.
*
* #param filename file to read from
* #param text character buffer to read into
*
* #return the number of bytes read.
*/
long read_file(char *filename, char *buff)
{
FILE *fp = fopen(filename, "r");
long size = 0; // Number of characters read.
int len = 0;
if (fp == NULL)
{
fprintf(stderr,"1 Error could not open file: %s\n",strerror(errno));
return -1;
}
/* Go to the end of the file. */
if (fseek(fp, 0L, SEEK_END) == 0)
{
/* Get the size of the file. */
size = ftell(fp);
if (size == -1)
{
fprintf(stderr,"2 Error could not open file: %s\n",strerror(errno));
return -1;
}
/* Go back to the start of the file. */
if (fseek(fp, 0L, SEEK_SET) != 0)
{
fprintf(stderr,"3 Error rewinding to start of file: %s\n",strerror(errno));
return -1;
}
/* Read the entire file into memory. */
len = fread(buff, sizeof(char), (size_t)size, fp);
if (len == 0)
{
fprintf(stderr,"4 Error reading file into memory: %s\n",strerror(errno));
return -1;
}
else
{
buff[++len] = '\0'; /* Add a null-terminator. */
}
}
(void)fclose(fp);
return size;
}
int compute_words(char* fileloc)
{
int wordcount = 0;
int check = 1;
char file;
FILE *f = fopen(fileloc, "r");
while((file=getc(f)) != EOF)
{
if(isspace(file) || file == '\t' || file == '\n')
{
if (check == 0)
{
check++;
wordcount++;
}
}
else
{
check = 0;
}
}
fclose(f);
return wordcount;
}
int compute_lines(char* fileloc)
{
int linecount = 0;
char file;
FILE *f = fopen(fileloc, "r");
while((file=getc(f)) != EOF)
{
if(file == '\n')
linecount++;
}
fclose(f);
return linecount;
}
/* The name of this program. */
const char* program_name;
/* Prints usage information for this program to STREAM (typically
stdout or stderr), and exit the program with EXIT_CODE. Does not
return. */
void print_usage (FILE* stream, int exit_code)
{
fprintf (stream, "Usage: %s options [ inputfile .... ]\n", program_name);
fprintf (stream,
" -h --help Display this usage information.\n"
" -n --num Display my student number.\n"
" -c --chars Print number of characters in FILENAME.\n"
" -w --words Print number of words in FILENAME.\n"
" -l --lines Print number of lines in FILENAME.\n"
" -f --file FILENAME Read from file.\n");
exit (exit_code);
}
/* Main program entry point. ARGC contains number of argument list
elements; ARGV is an array of pointers to them. */
int main (int argc, char* argv[])
{
int pipes[2][2];
pid_t child[2];
int status = 0;
int i;
//printf("\nParents Pro ID is %d\n\n", getpid());
char* fileloc = "/usr/share/dict/words";
char buffer[BUFFSIZE];
char* buff = &buffer[0];
int num = 0, chars = 0, words = 0, lines = 0;
int wordcount = 0;
int linecount = 0;
int next_option;
/* A string listing valid short options letters. */
const char* const short_options = "hncwlf:";
/* An array describing valid long options. */
const struct option long_options[] = {
{ "help", 0, NULL, 'h' },
{ "num", 0, NULL, 'n' },
{ "chars", 0, NULL, 'c' },
{ "words", 0, NULL, 'w' },
{ "lines", 0, NULL, 'l' },
{ "file", 1, NULL, 'f' },
{ NULL, 0, NULL, 0 } /* Required at end of array. */};
/* The name of the file to receive program output, or NULL for
standard output. */
const char* output_filename = NULL;
/* Remember the name of the program, to incorporate in messages.
The name is stored in argv[0]. */
program_name = argv[0];
do
{
next_option = getopt_long (argc, argv, short_options,long_options, NULL);
switch (next_option)
{
case 'h': /* -h or --help */
/* User has requested usage information. Print it to standard
output, and exit with exit code zero (normal termination). */
print_usage (stdout, 0);
case 'n':
num=1;
break;
case 'c':
chars=1;
break;
case 'w':
words=1;
break;
case 'l':
lines=1;
break;
case 'f':
fileloc = optarg;
break;
case '?': /* The user specified an invalid option. */
/* Print usage information to standard error, and exit with exit
code one (indicating abnormal termination). */
print_usage (stderr, 1);
case -1: /* Done with options. */
if(!num && !chars && !words && !lines)
chars=1;words=1;lines=1;
break;
default: /* Something else: unexpected. */
abort ();
}
}
while (next_option != -1);
for(i = 0; i < 3; i++)
{
if (pipe(pipes[i]) != 0)
{
printf("Error pipe %d could not be created\n", i);
exit(1);
}
if ((child[i] = fork()) == -1)//create fork
{
printf("Error fork %d could not be created\n", i);
exit(1);
}
else if (child[i] == 0) //fork successful
{
close(pipes[i][0]);
if(words && child[0]) //child 1
{
int computewords = compute_words(fileloc);
write(pipes[0][1], &computewords, sizeof(computewords));
}
if(lines && child[1]) //child 2
{
int computelines = compute_lines(fileloc);
write(pipes[1][1], &computelines, sizeof(computelines));
}
exit(0);
}
}
for (i = 0; i < 2; i++)
{
wait(&status);
}
if(num)
{
char *z=getenv("USER");
if(z == NULL) return EXIT_FAILURE;
printf("\nStudent number: 12345 and logged in as %s\n", z);
}
if(chars)
printf("\nNumber of Characters in the file:%s:\t%ld\n", fileloc, read_file(fileloc, buff));
if(words)
{
close(pipes[0][1]);
read(pipes[0][0], &wordcount, 50);
close(pipes[0][0]);
printf("\nNumber of Words in the file:%s:\t%d\n", fileloc, wordcount);
}
if(lines)
{
close(pipes[1][1]);
read(pipes[1][0], &linecount, 50);
close(pipes[1][0]);
printf("\nNumber of Lines in the file:%s:\t%d\n", fileloc, linecount);
}
close(pipes[0][0]);
close(pipes[1][0]);
close(pipes[0][1]);
close(pipes[1][1]);
return 0;
}
There's something else going on here - an if statement will work if you're getting the expected arguments. Try debugging the main program as it appears you have an error in your option parsing.
Consider the following case statement:
case -1: /* Done with options. */
if(!num && !chars && !words && !lines)
chars=1;words=1;lines=1;
break;
You have an if without braces around the assignments. Just because the statements are on the same line, doesn't mean the parser understands your intent. Instead it'll be parsed as such:
case -1: /* Done with options. */
if(!num && !chars && !words && !lines)
chars=1;
words=1;
lines=1;
break;
Which certainly will lead to unexpected behavior.
if(!num && !chars && !words && !lines)
chars=1;words=1;lines=1;
is equivalent to
if(!num && !chars && !words && !lines)
chars=1;
words=1;
lines=1;
You need some braces, or to put everything in a single statement like this:
if(!num && !chars && !words && !lines)
chars=words=lines=1;
I have a problem with my program to get it run correctly.
here is the code:
#include <stdio.h>
#include <stdlib.h> // for EXIT_SUCCESS and EXIT_FAILURE
#include <ctype.h>
#include <string.h>
void ReadFile(FILE* file) {
unsigned lines = 0;
int braces = 0;
int curlyBraces = 0;
int comments = 0;
int c;
char* line = 0;
unsigned col = 0;
while ((c = fgetc(file)) != EOF) {
if(c == '\n') { // new line
lines++;
printf("%4d: {%d} (%d) /*%d*/ |%s\n", lines, curlyBraces, braces, comments, line);
free(line); line = 0;
col = 0;
} else {
// add character to line
line = (char*)realloc(line, (col+1)*sizeof(char));
if (line == 0) {
fprintf(stderr, "error reallocating memory");
return;
}
line[col] = c;
col++;
if (c == '(') {
braces++;
} else if (c == ')') {
braces--;
} else if (c == '{') {
curlyBraces++;
} else if (c == '}') {
curlyBraces--;
} else if (c == '/') {
if (fgetc(file) == '*') {
comments++;
} else {
fseek(file, -1, SEEK_CUR);
}
} else if (c == '*') {
if (fgetc(file) == '/') {
comments--;
} else {
fseek(file, -1, SEEK_CUR);
}
}
}
}
}
int main(int argc, char** argv) {
short lines = 0, words = 0, chars = 0;
/* check for arguments */
if (argc == 1) {
fprintf(stderr, "usage: %s filename\n", argv[0]);
return EXIT_FAILURE;
}
/* open file */
FILE* file = fopen(argv[1], "r");
if(file == 0) {
fprintf(stderr, "error open file '%s'\n", argv[1]);
return EXIT_FAILURE;
}
ReadFile(file);
if (fclose(file) == EOF) {
fprintf(stderr, "error in fclose()\n");
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
on the output i get some weird output, like realloc overwrites some data...
i already tried strcat, but i can't use constant chars. so i have to use realloc.
here is a short excerpt of the output
P 68: {1} (0) /*0*/ | / open file *
69: {1} (0) /*0*/ | FILE* file = fopen(argv[1], "r");
70: {2} (0) /*0*/ | if(file == 0) {
rn EXIT_FA(0) /*0*/ | fprintf(stderr, "error open file '%s'\n", argv[1]);
r open fi (0) /*0*/ | return EXIT_FAILURE;
73: {1} (0) /*0*/ | }
} 74: {1} (0) /*0*/ |
maybe there is another way to reaize this? with fgets() i could get the whole line, but increments the pointer in the file and i have to give fgets() a count of chars. so that wouldn't be the perfect solution.
You need to terminate your string before you print it out:
lines++;
line[col] = 0; // new
printf("%4d: {%d} (%d) /*%d*/ |%s\n", lines, curlyBraces, braces, comments, line);
Unfortunately line[col] is out of bounds here. So you need realloc line before adding the terminator like this:
lines++;
line = (char*)realloc(line, (col+1)*sizeof(char));
if (line == 0) {
fprintf(stderr, "error reallocating memory");
return;
}
line[col] = 0; // new
printf("%4d: {%d} (%d) /*%d*/ |%s\n", lines, curlyBraces, braces, comments, line);
Also, do you know about ungetc? You can replace those fseek(-1) with ungetc.
I'm trying to get 2 way communication between a main file and a helper file.
The main file forks, and the child does some pipe work and then runs an exec.
My problem is that I can send information from the child exec to the parent exec, but not the other way around.
Below Is my entire code from the two files, so you should be able to run it.
Any help in getting the 2 way communication working will be extremely helpful. i'm been at this for almost 8 hours straight now.
When you run it, you'll see it print out "yo 0". This was me testing that it takes an integer from the main file, sends it to the helper, adds yo in front of it and sends it back. The first slab of code is the main file, second is the helper, third is the map file needed to run it. make sure there isn't a blank line underneath the last line, and the fourth is the agent file needed to run it.
the running is [./handler mapfile 20 agentfile.]
the int 20 doesn't do anything yet, but you need it in there to run the file.
If anyone actually goes to the effort to do all this and help me, i am eternally grateful
main file (handler.c)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/wait.h>
enum ErrorCode {
SHOW_USAGE = 1, BAD_STEPS, OPEN_MAP_ERROR, CORRUPT_MAP,
OPEN_AGENT_ERROR, CORRUPT_AGENTS, AGENT_ERROR,
AGENT_WALLED, AGENT_COLLIDED, TOO_MANY_STEPS, INVALID_AGENT_RESPONSE,
AGENT_CLOSED, AGENT_DIED, SIGINT_REC
};
typedef struct {
int valid;
int row, col;
} Point;
typedef struct {
Point point;
int number;
char name;
char param[20];
char type[20];
} Agent;
typedef struct {
int rows, cols;
char **grid;
} Map;
Map map;
Map agentMap;
int listSize = 0;
void error(enum ErrorCode e) {
switch(e) {
case SHOW_USAGE:
fprintf(stderr, "Usage: handler mapfile maxsteps agentfile\n");
break;
case BAD_STEPS:
fprintf(stderr, "Invalid maxsteps.\n");
break;
case OPEN_MAP_ERROR:
fprintf(stderr, "Unable to open map file.\n");
break;
case CORRUPT_MAP:
fprintf(stderr, "Corrupt map.\n");
break;
case OPEN_AGENT_ERROR:
fprintf(stderr, "Unable to open agent file.\n");
break;
case CORRUPT_AGENTS:
fprintf(stderr, "Corrupt agents.\n");
break;
case AGENT_ERROR:
fprintf(stderr, "Error running agent.\n");
break;
case AGENT_WALLED:
fprintf(stderr, "Agent walled.\n"); // needs fixing, check spec sheet
break;
case AGENT_COLLIDED:
fprintf(stderr, "Agent collided.\n"); // same as AGENT_WALLED
break;
case TOO_MANY_STEPS:
fprintf(stderr, "Too many steps.\n");
break;
case INVALID_AGENT_RESPONSE:
fprintf(stderr, "Agent sent invalid response.\n"); // fixiing
break;
case AGENT_CLOSED:
fprintf(stderr, "Agent exited with status.\n"); // fixiing
break;
case AGENT_DIED:
fprintf(stderr, "Agent exited due to signal.\n"); // fixing
break;
case SIGINT_REC:
fprintf(stderr, "Exiting due to INT signal.\n");
break;
}
exit(e);
}
void print_map(Map map)
{
int r;
for (r = 0; r < map.rows; ++r) {
printf("%s", map.grid[r]);
}
puts("");
}
void print_agents(Agent *agents, int size)
{
int i;
for (i = 0; i < size; i++) {
Agent temp = agents[i];
printf("%d %d %c %d %s %s %i\n", temp.point.row, temp.point.col, temp.name, temp.number, temp.type, temp.param, i);
}
puts("");
}
void readMap(char *file)
{
int r;
FILE *fd = fopen(file, "r");
char buffer[20];
char d;
if (!fd) {
error(OPEN_MAP_ERROR);
}
if (fgets(buffer, 20, fd) == NULL) {
error(CORRUPT_MAP);
}
if (sscanf(buffer, "%d %d%1[^\n]\n", &map.rows, &map.cols, &d) != 2 ||
map.rows < 1 || map.rows > 999 || map.cols < 1 || map.cols > 999) {
error(CORRUPT_MAP);
}
map.grid = malloc(map.rows * sizeof(char *));
for (r = 0; r < map.rows; ++r) {
map.grid[r] = calloc(map.cols + 2, sizeof(char));
if (fgets(map.grid[r], map.cols + 2, fd) == NULL ||
map.grid[r][map.cols] != '\n') {
error(CORRUPT_MAP);
}
}
fclose(fd);
}
void checkAgent(char *file)
{
FILE *fd = fopen(file, "r");
if (!fd) {
error(AGENT_ERROR);
}
fclose(fd);
}
int growList (Agent **agentList, int curSize, int increaseNum)
{
const int newSize = curSize + increaseNum;
Agent *temp = (Agent*) realloc(*agentList, (newSize * sizeof(Agent)));
if (temp == NULL) {
exit(20);
}
else {
*agentList = temp;
return newSize;
}
}
Agent* readAgentFile(char *file, Agent *agentList)
{
int readCount = 0;
FILE *fp = fopen(file, "r");
char buffer[80];
listSize = 0;
if (!fp) {
error(OPEN_AGENT_ERROR);
}
if (fgets(buffer, 80, fp) == NULL) {
error(CORRUPT_AGENTS);
}
rewind(fp);
while (fgets(buffer, 80, fp) != NULL) {
if (buffer[0] != '#') {
Agent agent;
sscanf( buffer, "%d %d %c %s %s" ,&agent.point.row, &agent.point.col, &agent.name, agent.type, agent.param);
checkAgent(agent.type);
agent.number = readCount+1;
listSize = growList(&agentList, listSize, 1);
agentList[readCount] = agent;
readCount++;
}
}
if (readCount == 0) {
error(CORRUPT_AGENTS);
}
fclose(fp);
return agentList;
}
void createAgentMap()
{
int i,j;
agentMap = map;
for (i=0; i < map.rows; i++) {
for (j=0; j < map.cols; j++) {
char c = map.grid[i][j];
if (c == '.') {
agentMap.grid[i][j] = ' ';
}
}
}
}
int main(int argc, char **argv)
{
int steps;
int pid;
int returnStatus;
int i;
int out_pipe[2];
int in_pipe[2];
char ch[20];
Agent firstAgent;
Agent *agentList =(Agent *) calloc(1, sizeof(Agent));
if (argc != 4) {
error(SHOW_USAGE);
}
sscanf(argv[2], "%d", &steps);
if ((steps < 1)) {
error(BAD_STEPS);
}
readMap(argv[1]);
agentList = readAgentFile(argv[3], agentList);
firstAgent = agentList[0];
createAgentMap();
for (i=0; i < listSize; i++) {
if (pipe(out_pipe) < 0) {
perror("Pipe Error");
}
if (pipe(in_pipe) < 0) {
perror("Child pipe error");
}
Agent temp;
temp = agentList[i];
switch ( pid = fork() )
{
case -1:
perror("Can't fork.\n");
exit(20);
case 0:
/* Child */
/*close(1);
dup(in_pipe[1]);
close(0);
dup(out_pipe[0]);
close(in_pipe[0]);
close(out_pipe[1]);*/
dup2(out_pipe[0], 0);
dup2(in_pipe[1], 1);
execlp(temp.type, temp.type, temp.param, (char *)0);
perror("No exec");
default:
//close(1);
//dup(handlerChild[1]);
//fprintf(stdout, "%d", listSize);
write(out_pipe[1], "%d", listSize);
close(in_pipe[1]);
close(0);
dup(in_pipe[0]);
if (fgets(ch, 20, stdin) == NULL) {
break;
}
printf("%s\n", ch);
}
}
while (steps > 0) {
steps -= 1;
}
return 0;
}
helper file (simple.c)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
typedef struct {
int valid;
int row, col;
} Point;
typedef struct {
int numAgents;
char agentNames[80];
int agentNumber;
} Info;
typedef struct {
int rows, cols;
char **grid;
} Map;
Map agent_map;
int main(int argc, char **argv)
{
int steps = 10;
int simple_pipe[2];
int dir;
char inputDir;
char input_stream[20];
int in = dup(0);
Info info;
if (argc == 2) {
sscanf(argv[1], "%c1", &inputDir);
switch (inputDir) {
case 'N': dir = 0; break;
case 'E': dir = 1; break;
case 'S': dir = 2; break;
case 'W': dir = 3; break;
default : fprintf(stdout, "Invalid params.\n"); exit(2);
}
}
else {
fprintf(stdout, "Incorrect number of params.\n");
exit(1);
}
close(0);
dup(simple_pipe[0]);
fgets(input_stream, 20, stdin);
sscanf(input_stream, "%d", &info.numAgents);
//printf("%d", info.numAgents);
//printf("this is the input: %s\n", input_stream); // This is successfully printing to stdout in the pipe
fprintf(stderr, "yo %d \n", info.numAgents);
while (steps > 0) {
steps -= 1;
}
exit(0);
}
map file
6 6
##..##
#....#
#.##.#
#....#
##....
######
agent file
1 1 A ./simple E
2 2 B ./simple N
5 2 C ./simple S
A pipe is a unidrectional connection across processes. Before you fork, you open the pipe and it will reserve two file descriptors, where fd[0] can be read from and fd[1] can be written to.
So when you want to have a two way commumincation you need to create two pipes, and then use one for reading in the parent writing in the child and the second pipe the other way around.
A more detailed explanation along with some sample code can be foun dhere: http://linux.die.net/man/2/pipe
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
int c, n, E, b, s, v, t, opt, valid = 0;
char current = '\0';
char previous = '\0';
FILE *fp;
/* -n numbers lines
* -E appends a dollar sign to line ends
* -b numbers only non-blank lines
* -s squeezes multiple blank lines down to 1
* -v displays control chars, excluding tab
* -t includes tab in the above
* -e is the same as -E and -v
*/
int setFlags(int argc, char *argv[]) {
int op;
while ((op = getopt(argc, argv, "nEbsvte")) != -1) {
switch (op) {
case 'n': {
n = 1;
break;
} case 'E': {
E = 1;
break;
} case 'b': {
b = 1;
break;
} case 's': {
s = 1;
break;
} case 'v': {
v = 1;
break;
} case 't': {
t = 1;
break;
} case 'e': {
E = 1;
v = 1;
break;
} case '?': {
//fprintf(stderr, "Option `-%c` is not valid.\n", optopt);
return EXIT_FAILURE;
} default: {
abort();
}
}
}
opt = optind;
if(n == 1) {
b = 0;
}
return EXIT_SUCCESS;
}
int checkFile(char *path) {
if (access(path, R_OK) == 0) {
return EXIT_SUCCESS;
} else {
fprintf(stderr, "cat: %s: %s\n", argv[i], strerror(errno));
errno = 0;
return EXIT_FAILURE;
}
}
int doPrint(char *path) {
if (strcmp(path, "stdin") == 0) {
fp = stdin;
} else {
if (checkFile(path) == 1) {
return EXIT_FAILURE;
} else {
fp = fopen(path, "r");
}
}
while ((c = fgetc(fp)) != EOF) {
putchar(c);
}
fclose(fp);
return EXIT_SUCCESS;
}
int main (int argc, char *argv[]) {
if (setFlags(argc, argv) == 1) {
fprintf(stderr, "The program has terminated with an error.\n"
"An invalid option was specified.\n");
return EXIT_FAILURE;
} else {
if ((argc - opt) == 0) {
doPrint("stdin");
} else {
for(int i = opt; i < argc; i++) {
doPrint(argv[i]);
}
}
}
}
I'm getting a really crazy bug, where my program outputs the error line in checkFile, before it finishes writing the contents of the file (always one chat before the end).
It's driving me insane, and no matter where I move that piece of code, it doesn't work as intended.
I'm sure the answer is probably trivial, but it has me stumped. I'd even thrown in sleeps and various other things just before output finished, and it would throw the error, THEN sleep, THEN print the final character.
Any help?
When using printf, stdout output is buffered by default. This means it can be interleaved with other output, often from stderr. stderr is unbuffered by default so that it's output is printed immediately as would normally be desired when an error occurs.
Interleaving can be fixed with judicious use of fflush or by turning off file buffering of stdout using setbuf. Be sure to read the man pages for setbuf as there are some caveats.
In this case, adding fflush(stdout) at the end of the doPrint function should fix the "problem".