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The tee utility copies its standard input to both stdout and to a file. This allows the user to view the output of a command on the console while writing a log to a file at the same time.
My program implements the tee command from linux POSIX system calls, with the -a option.
How can I modify the program to test for possible memory allocation errors? Positive memory leaks.
Also, the memory allocation doesn't seem right to me. When creating a new buffer each time I call getline(), should I declare and initialize line outside the loop and reallocate it only after the loop has ended?
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <fcntl.h>
#include <sys/stat.h>
#include "apue.h"
int writeAll(int fd, char *buf, int buflen);
int main(int argc, char *argv[]) {
struct stat status;
int option;
bool append = false;
int errCode = 0;
while ((option = getopt(argc, argv, "a")) != -1) {
switch (option) {
case 'a':
append = true;
break;
}
}
// We need to write in all the files given as parameter AND stdout.
int numFileDescriptors = argc - optind + 1;
int *fileDescriptors = malloc((numFileDescriptors + 1) * sizeof(*fileDescriptors));
char **fileNames = malloc((numFileDescriptors + 1) * sizeof(*fileNames));
int lastFileDescriptor = 0;
fileDescriptors[0] = STDOUT_FILENO;
fileNames[0] = "stdout";
int flags = O_CREAT | O_WRONLY;
if (append) {
flags = flags | O_APPEND;
} else {
flags = flags | O_TRUNC;
}
for (int i = optind; i < argc; i++) {
if (access(argv[i], F_OK) == 0) {
if (access(argv[i], W_OK) < 0) {
err_msg("%s: Permission denied", argv[i]);
errCode = 1;
continue;
}
}
if (lstat(argv[i], &status) < 0) {
status.st_mode = 0;
}
if (S_ISDIR(status.st_mode)) {
err_msg("%s: Is a directory", argv[i]);
errCode = 1;
continue;
}
int fd = open(argv[i], flags, 0644);
if (fd < 0) {
err_msg("%s: Failed to open", argv[i]);
errCode = 1;
continue;
}
lastFileDescriptor = lastFileDescriptor + 1;
fileDescriptors[lastFileDescriptor] = fd;
fileNames[lastFileDescriptor] = argv[i];
}
while (true) {
size_t len = 0;
ssize_t read = 0;
char *line = NULL;
read = getline(&line, &len, stdin);
if (read == -1) {
break;
}
for (int i = 0; i <= lastFileDescriptor; i++) {
int written = writeAll(fileDescriptors[i], line, strlen(line));
if (written < 0) {
err_msg("%s: Failed to write", fileNames[i]);
errCode = 1;
}
}
}
for (int i = 0; i <= lastFileDescriptor; i++) {
close(fileDescriptors[i]);
}
free(fileDescriptors);
free(fileNames);
return errCode;
}
int writeAll(int fd, char *buf, int buflen) {
ssize_t written = 0;
while (written < buflen) {
int writtenThisTime = write(fd, buf + written, buflen - written);
if (writtenThisTime < 0) {
return writtenThisTime;
}
written = written + writtenThisTime;
}
return written;
}
Testing for memory allocation failure is simple: just add tests, report the failure and exit with a non zero exit status.
To avoid memory leaks, you must free the line that was allocated by getline inside the while (true) loop:
while (true) {
size_t len = 0;
char *line = NULL;
ssize_t nread = getline(&line, &len, stdin);
if (nread == -1) {
if (errno == ENOMEM) {
fprintf(stderr, "out of memory\n");
exit(1);
}
free(line);
break;
}
for (int i = 0; i <= lastFileDescriptor; i++) {
int written = writeAll(fileDescriptors[i], line, nread);
if (written < 0) {
err_msg("%s: Failed to write", fileNames[i]);
errCode = 1;
}
}
free(line);
}
Alternately, you can reuse the same line for the next iteration and only free the buffer after the while loop:
size_t len = 0;
char *line = NULL;
while (true) {
ssize_t nread = getline(&line, &len, stdin);
if (nread == -1) {
if (errno == ENOMEM) {
fprintf(stderr, "out of memory\n");
exit(1);
}
break;
}
for (int i = 0; i <= lastFileDescriptor; i++) {
int written = writeAll(fileDescriptors[i], line, nread);
if (written < 0) {
err_msg("%s: Failed to write", fileNames[i]);
errCode = 1;
}
}
}
free(line);
Note that reading a full line at a time is risky as the input might contain very long, possibly unlimited lines (eg: /dev/zero). You might want to use fgets() to read a line with a limited length and dispatch the contents as you read, possibly splitting long lines:
char line[4096];
while (fgets(line, sizeof line, stdin)) {
size_t len = strlen(line);
for (int i = 0; i <= lastFileDescriptor; i++) {
int written = writeAll(fileDescriptors[i], line, len);
if (written < 0) {
err_msg("%s: Failed to write", fileNames[i]);
errCode = 1;
}
}
}
The above code has a limitation: if the input streams contains null bytes, they will cause some data to be lost in translation. A solution is to not use fgets(), but getchar() directly:
for (;;) {
char line[4096];
size_t len = 0;
int c;
while (len < sizeof(line) && (c = getchar()) != EOF)) {
if ((line[len++] = c) == '\n')
break;
}
if (len > 0) {
for (int i = 0; i <= lastFileDescriptor; i++) {
int written = writeAll(fileDescriptors[i], line, len);
if (written < 0) {
err_msg("%s: Failed to write", fileNames[i]);
errCode = 1;
}
}
}
if (c == EOF)
break;
}
I wrote a program, which reads from a file. I use a condition in which I print that the array is too big, but when I use a too big array instead of showing this message I have segmentation fault.
This is my program
#include <stdio.h>
#include <stdlib.h>
#define N 10000 // Maximum array size
int _strlen(char *array) {
int i;
for (i = 0; array[i] != '\0'; ++i);
return i;
}
int readText(FILE *wp, char *s, int max) {
int sum = 0;
if (_strlen(s) > max) {
printf("This array is too big. Maximum size is %d", max);
} else {
while ((*s++ = fgetc(wp)) != EOF) {
sum++;
}
*(s-1) = '\0';
}
return sum;
}
int main(int argc, char *argv[]) {
FILE *wz, *wc;
char *s;
char array[N];
s = array;
if (argc != 3) {
printf("Wrong arguments number\n");
printf("I should run this way:\n");
printf("%s source result\n",argv[0]);
exit(1);
}
if ((wz = fopen(argv[1], "r")) == NULL) {
printf("Open error %s\n", argv[1]);
exit(1);
}
if ((wc = fopen(argv[2], "w")) == NULL) {
printf("Open error %s\n", argv[2]);
exit(2);
}
fprintf(wc, "Read text from file source.txt");
readText(wz, s, 10000);
return 0;
}
In output I want to have: This array is too big. Maximum size is %d
Instead of Segmentation fault core dumped
In addition, I want to say that the program is when I use a smaller array, but I want to show the user a proper message when he uses too big array instead of segmentation fault.
Thanks, I change my program in that way. The only problem is that this program check the if condition in every while loop so this program could be slow.
int readText(FILE *wp, char *s, int max) {
int sum = 0;
if (_strlen(s) > max) {
printf("This array is too big. Maximum size is %d", max);
} else {
while ((*s++ = fgetc(wp)) != EOF) {
sum++;
if (sum > max) {
printf("This array is too big. Maximum size is %d", max);
break;
}
}
*(s-1) = '\0';
}
return sum;
}
The remarks / other answer solve your undefined behavior (segmentation fault in your case).
The only problem is that this program check the if condition in every while loop so this program could be slow.
Your program is not slow because of a 'if' but because you read the file char per char.
Using stat or equivalent function you can get the size of the file to read it throw only one fread :
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/stat.h>
#define N 10000 // Maximum array size
int main(int argc, char *argv[]) {
char array[N];
FILE *wz, *wc;
struct stat st;
off_t sz;
if (argc != 3) {
printf("Wrong arguments number\n"
"I should run this way:\n"
"%s source result\n", argv[0]);
exit(1);
}
if ((wz = fopen(argv[1], "r")) == NULL) {
printf("Cannot open %s to read : %s\n", argv[1], strerror(errno));
exit(1);
}
if (stat(argv[1], &st) == -1) {
printf("Cannot get stat of %s : %s\n", argv[1], strerror(errno));
exit(1);
}
if (st.st_size > N-1) {
printf("This array is too big. Maximum size is %d", N-1);
sz = N-1;
}
else
sz = st.st_size;
if (fread(array, 1, sz, wz) != sz) {
printf("cannot read %s : %s", argv[1], strerror(errno));
fclose(wz); /* for valgrind end test etc */
exit(1);
}
array[sz] = 0;
fclose(wz);
if ((wc = fopen(argv[2], "w")) == NULL) {
printf("Cannot open %s to write : %s\n", argv[2], strerror(errno));
fclose(wz); /* for valgrind end test etc */
exit(2);
}
/* ... */
fclose(wc);
return 0;
}
Knowing the size of the file allows to remove that limitation to a constant size and try to read the file while you can allocate enough memory for :
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/stat.h>
int main(int argc, char *argv[]) {
char * array;
FILE *wz, *wc;
struct stat st;
if (argc != 3) {
printf("Wrong arguments number\n"
"I should run this way:\n"
"%s source result\n", argv[0]);
exit(1);
}
if ((wz = fopen(argv[1], "r")) == NULL) {
printf("Cannot open %s to read : %s\n", argv[1], strerror(errno));
exit(1);
}
if (stat(argv[1], &st) == -1) {
printf("Cannot get stat of %s : %s\n", argv[1], strerror(errno));
exit(2);
}
if ((array = malloc(st.st_size + 1)) == NULL) {
printf("Not enough memory to memorize the file %s\n", argv[1]);
exit(3);
}
if (fread(array, 1, st.st_size, wz) != st.st_size) {
printf("cannot read %s : %s", argv[1], strerror(errno));
fclose(wz); /* for valgrind end test etc */
free(array); /* for valgrind etc */
exit(4);
}
array[st.st_size] = 0;
fclose(wz);
if ((wc = fopen(argv[2], "w")) == NULL) {
printf("Cannot open %s to write : %s\n", argv[2], strerror(errno));
free(array); /* for valgrind etc */
exit(5);
}
/* ... */
fclose(wc);
free(array); /* for valgrind etc */
return 0;
}
Anyway because of the usage of the program "source result" may be you want to copy the file specified by argv[1] in the file specified by argv[2], in that case better to read and write block by block rather than to read all to not use a lot of memory for nothing and to manage the case the input file size is greater than the memory size.
You cannot measure the length of the destination array with _strlen(s), the size is given as an argument and reading an uninitialized array with _strlen() has undefined behavior.
Furthermore, you store fgetc(fp) to *s++ before testing for EOF. This is incorrect in all cases:
if char type is signed, EOF cannot be distinguished from a valid byte value of \377.
if char is unsigned, EOF cannot be tested because it has been converted as a char value of 0xff, hence the loop runs forever, writing beyond the end of the destination array until this causes a crash.
You simply want to add a test in the reading loop to stop reading bytes from the file when the buffer is full and read the bytes into an int variable so you can test for end of file reliably.
Here is a modified version:
#include <stdio.h>
#include <stdlib.h>
#define N 10000 // Maximum array size
int readText(FILE *wp, char *s, int max) {
int i = 0, c;
while (i < max - 1 && (c = fgetc(wp)) != EOF) {
s[i++] = c;
}
s[i] = '\0';
return i;
}
int main(int argc, char *argv[]) {
FILE *wz, *wc;
char array[N];
int nread;
if (argc != 3) {
printf("Wrong arguments number\n");
printf("I should run this way:\n");
printf("%s source result\n", argv[0]);
exit(1);
}
if ((wz = fopen(argv[1], "r")) == NULL) {
printf("Open error %s\n", argv[1]);
exit(1);
}
if ((wc = fopen(argv[2], "w")) == NULL) {
printf("Open error %s\n", argv[2]);
exit(2);
}
fprintf(wc, "Read text from file source.txt\n");
nread = readText(wz, array, N);
printf("Read %d bytes\n", nread);
return 0;
}
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'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".