How to find a line in a file using regex in C? - c

how can i use Regex Expressions in C programming?
for example if i want to find a line in a file
DAEMONS=(sysklogd network sshd !netfs !crond)
then print each daemon in separate line like this
sysklogd
network
sshd
!netfs
!crond
here what i did so far
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <regex.h>
#define tofind "[a-z A-Z] $"
int main(){
FILE *fp;
char line[1024];
int retval = 0;
char address[256];
regex_t re;
if(regcomp(&re, tofind, REG_EXTENDED) != 0)
return;
fp = fopen("/etc/rc.conf","r");//this file has this line "DAEMONS=(sysklogd network sshd !netfs !crond)"
while((fgets(line, 1024, fp)) != NULL) {
if((retval = regexec(&re, address, 0, NULL, 0)) == 0)
printf("%s\n", address);
}
}
Any help would be much appreciated.

You read the line into line, so you should pass line to regexec(). You also need to think about whether the newline at the end of the line affects the patterns. (It was correct to use fgets(), but remember it keeps the newline at the end.)
You should also do return -1; (or any other value that is not 0 modulo 256) rather than a plain return with no value. Also, you should check that the file was opened; I had to use an alternative name because there is no such file as /etc/rc.conf on my machine - MacOS X.
This works for me:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <regex.h>
#define tofind "[a-z A-Z] $"
int main(int argc, char **argv)
{
FILE *fp;
char line[1024];
int retval = 0;
regex_t re;
//this file has this line "DAEMONS=(sysklogd network sshd !netfs !crond)"
const char *filename = "/etc/rc.conf";
if (argc > 1)
filename = argv[1];
if (regcomp(&re, tofind, REG_EXTENDED) != 0)
{
fprintf(stderr, "Failed to compile regex '%s'\n", tofind);
return EXIT_FAILURE;
}
fp = fopen(filename, "r");
if (fp == 0)
{
fprintf(stderr, "Failed to open file %s (%d: %s)\n",
filename, errno, strerror(errno));
return EXIT_FAILURE;
}
while ((fgets(line, 1024, fp)) != NULL)
{
line[strlen(line)-1] = '\0';
if ((retval = regexec(&re, line, 0, NULL, 0)) == 0)
printf("<<%s>>\n", line);
}
return EXIT_SUCCESS;
}
If you need help writing regular expressions instead of help writing C code that uses them, then we need to design the regex to match the line you show.
^DAEMONS=([^)]*) *$
This will match the line as long as it is written as shown. If you can have spaces between the 'S' and the '=' or between the '=' and the '(', then you need appropriate modifications. I've allowed for trailing blanks - people are often sloppy; but if they use trailing tabs, then the line won't be selected.
Once you've found the line, you have to split it into pieces. You might elect to use the 'capturing' brackets facility, or simply use strchr() to find the open bracket, and then a suitable technique for separating the daemon names - I'd avoid strtok() and probably use strspn() or strcspn() to find the words.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <regex.h>
#define tofind "^DAEMONS=\\(([^)]*)\\)[ \t]*$"
int main(int argc, char **argv)
{
FILE *fp;
char line[1024];
int retval = 0;
regex_t re;
regmatch_t rm[2];
//this file has this line "DAEMONS=(sysklogd network sshd !netfs !crond)"
const char *filename = "/etc/rc.conf";
if (argc > 1)
filename = argv[1];
if (regcomp(&re, tofind, REG_EXTENDED) != 0)
{
fprintf(stderr, "Failed to compile regex '%s'\n", tofind);
return EXIT_FAILURE;
}
fp = fopen(filename, "r");
if (fp == 0)
{
fprintf(stderr, "Failed to open file %s (%d: %s)\n", filename, errno, strerror(errno));
return EXIT_FAILURE;
}
while ((fgets(line, 1024, fp)) != NULL)
{
line[strlen(line)-1] = '\0';
if ((retval = regexec(&re, line, 2, rm, 0)) == 0)
{
printf("<<%s>>\n", line);
printf("Line: <<%.*s>>\n", (int)(rm[0].rm_eo - rm[0].rm_so), line + rm[0].rm_so);
printf("Text: <<%.*s>>\n", (int)(rm[1].rm_eo - rm[1].rm_so), line + rm[1].rm_so);
char *src = line + rm[1].rm_so;
char *end = line + rm[1].rm_eo;
while (src < end)
{
size_t len = strcspn(src, " ");
if (src + len > end)
len = end - src;
printf("Name: <<%.*s>>\n", (int)len, src);
src += len;
src += strspn(src, " ");
}
}
}
return EXIT_SUCCESS;
}
A good deal of debugging code in there - but it won't take you long to produce the answer you request. I get:
<<DAEMONS=(sysklogd network sshd !netfs !crond)>>
Line: <<DAEMONS=(sysklogd network sshd !netfs !crond)>>
Text: <<sysklogd network sshd !netfs !crond>>
Name: <<sysklogd>>
Name: <<network>>
Name: <<sshd>>
Name: <<!netfs>>
Name: <<!crond>>
Beware: when you want a backslash in a regex, you have to write two backslashes in the C source code.

Related

Redirect output of command line to a variable in C

Is there a way to redirect output of a command line which returns integer as an output to a variable in C?
for example, if the command is "cmd", then is there a way to redirect its output (an integer) and store it in variable in C?
I tried using popen and fgets but it seems to be working only with characters. Any suggestions?
It works perfectly fine with popen and fgets:
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
const char *cmd = argc > 1 ? argv[1] : "echo 42";
char buf[32];
FILE *fp = popen(cmd, "r");
if( fp == NULL ){
perror("popen");
return 1;
}
if( fgets(buf, sizeof buf, fp) == buf ){
int v = strtol(buf, NULL, 10);
printf("read: %d\n", v);
}
return 0;
}
If you want to convert a character string from the standard input, you could use fgets and then use atoi to convert the input to an integer.
If you want to convert the output of a command, let's say ls and store the output of the command to a variable, you could learn about fork, dup2, pipe, and exec function family.
More about this topic on this tutorial : Capture the output of a child in C. This tutorial also provide an example with popen if you want to keep things "high level".
Here is an even simpler example using popen() and fscanf():
#include <errno.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[]) {
FILE *fp = popen("date '+%s'", "r");
long seconds;
if (fp == NULL) {
fprintf(stderr, "popen failed: %s\n", strerror(errno));
return 1;
}
if (fscanf(fp, "%ld", &seconds) == 1) {
printf("epoch seconds: %ld\n", seconds);
pclose(fp);
return 0;
} else {
fprintf(stderr, "invalid program output\n");
pclose(fp);
return 1;
}
}

Segfault in getline

The following code is supposed to read the file "rules.txt" and write it to a device line by line.
The flow should be:
Read line from rules.txt
Echo it to device
The following code always end in segfault because of readline and I have no idea why:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/mman.h>
#define BUFFER_LENGTH 256
int main()
{
char *line;
size_t len = BUFFER_LENGTH;
int fd = open("./rules.txt", O_RDONLY);
if(fd == -1)
{ perror("open failed"); return 0; }
FILE* fout = fopen("/sys/class/Rule_Table_Class/Rule_Table_Class_Rule_Table_Device/sysfs_att", "w+");
if(fout == NULL)
{ close(fd); perror("fopen failed, log.txt is busy!"); return 0; }
while (1)
{
line = (char*) malloc(len*sizeof(char));
if(line==NULL){
perror("malloc failed!"); return 0;
}
int bytesRead = getline(&line, &len, fd);
if (bytesRead == -1)
{
perror("Failed to read the message from the device.");
return errno;
}
sprintf(line,"%s","lala");
printf("line = %s", line);
}
fclose(fout);
close(fd);
return 0;
}
EDIT:
I corrected the code and still get a segfault. Here is the corrected code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/mman.h>
#define BUFFER_LENGTH 256
int main()
{
FILE * fp;
char * line = NULL;
size_t len = 0;
ssize_t read;
fp = fopen("./rules.txt", "r");
if(fp == NULL)
{ perror("open failed"); return 0; }
FILE* fout = fopen("/sys/class/Rule_Table_Class/Rule_Table_Class_Rule_Table_Device/sysfs_att", "w+");
if(fout == NULL)
{ perror("fopen failed!"); return 0; }
while (1)
{
ssize_t bytesRead = getline(&line, &len, fp);
if (bytesRead == -1)
{
return 0;
}
printf("line = %s", line);
fprintf(line,"%s",fout);
}
fclose(fout);
fclose(fp);
return 0;
}
First of all, the proper core getline() loop is
/* FILE *in = fopen(..., "r"); */
char *line = NULL;
size_t size = 0;
while (1) {
ssize_t len = getline(&line, &size, in);
if (len < 0)
break;
/* You have 'len' chars at 'line', with line[len] == '\0'. */
}
so, it is not getline() that causes the segfault, it is your fprintf(line, "%s", fout); that should be either fprintf(fout, "%s", line); or just fputs(line, fout);, or fwrite(line, 1, bytesRead, fout); since the line can contain embedded NUL bytes that fprintf() and fputs() consider an end of string mark.
If we modify the code so that the source and target file names are taken as command-line arguments (with - denoting standard input or standard output), this is what I'd personally like to see:
/* SPDX-License-Identifier: CC0-1.0 */
/* This tells the GNU C library to expose POSIX features, including getline(). */
#define _POSIX_C_SOURCE 200809L
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
int main(int argc, char *argv[])
{
if (argc != 3 || !strcmp(argv[1], "-h") || !strcmp(argv[1], "--help")) {
const char *self = (argc > 0 && argv && argv[0] && argv[0][0]) ? argv[0] : "(this)";
fprintf(stderr, "\n");
fprintf(stderr, "Usage: %s [ -h | --help ]\n", self);
fprintf(stderr, " %s SOURCE TARGET\n", self);
fprintf(stderr, "\n");
fprintf(stderr, "This copies all content from SOURCE to TARGET, line by line.\n");
fprintf(stderr, "Use '-' for standard input source or standard output target.\n");
fprintf(stderr, "\n");
return EXIT_SUCCESS;
}
const char *srcpath = argv[1];
const char *dstpath = argv[2];
/* If the path is "-", set it to NULL. */
if (srcpath && !strcmp(srcpath, "-"))
srcpath = NULL;
if (dstpath && !strcmp(dstpath, "-"))
dstpath = NULL;
FILE *src, *dst;
/* Open source for reading. If srcpath is NULL, use stdin. */
if (srcpath) {
src = fopen(srcpath, "r");
if (!src) {
fprintf(stderr, "%s: %s.\n", srcpath, strerror(errno));
return EXIT_FAILURE;
}
} else {
src = stdin;
}
/* Open target for writing. If dstpath is NULL, use stdout. */
if (dstpath) {
dst = fopen(dstpath, "w");
if (!dst) {
fprintf(stderr, "%s: %s.\n", dstpath, strerror(errno));
fclose(src);
return EXIT_FAILURE;
}
} else {
dst = stdout;
}
char *line = NULL;
size_t size = 0;
unsigned long linenum = 0;
while (1) {
ssize_t len = getline(&line, &size, src);
if (len < 0)
break;
linenum++;
if (fwrite(line, 1, len, dst) != (size_t)len) {
fprintf(stderr, "%s: Write error on line %lu.\n", dstpath ? dstpath : "(standard output)", linenum);
fclose(dst);
fclose(src);
return EXIT_FAILURE;
}
}
/* Technically, we don't need to release dynamically allocated (non-shared) memory,
because we're just about to exit, and the OS will automagically do that for us.
We can do this at any point we want during the loop, too. */
free(line);
line = NULL;
size = 0;
/* We do not know why getline() returned -1. Check if an error occurred, and whether we're at end of input. */
if (ferror(src) || !feof(src)) {
fprintf(stderr, "%s: Read error on line %lu.\n", srcpath ? srcpath : "(standard input)", linenum);
fclose(dst);
fclose(src);
return EXIT_FAILURE;
}
/* Check if any write errors have occurred. */
if (ferror(dst)) {
fprintf(stderr, "%s: Write error on line %lu.\n", dstpath ? dstpath : "(standard output)", linenum);
fclose(dst);
fclose(src);
}
/* Read errors should not occur at close time, but it costs very little for us to test anyway. */
if (fclose(src)) {
fprintf(stderr, "%s: Read error on line %lu.\n", srcpath ? srcpath : "(standard input)", linenum);
fclose(dst);
return EXIT_FAILURE;
}
/* Write errors can occur at close time, if the output has been buffered, or the target is on
a remote filesystem. Again, it costs us very little to check. */
if (fclose(dst)) {
fprintf(stderr, "%s: Write error on line %lu.\n", dstpath ? dstpath : "(standard output)", linenum);
return EXIT_FAILURE;
}
/* No errors; target is an identical copy of the source file. */
fprintf(stderr, "%lu lines copied successfully.\n", linenum);
return EXIT_SUCCESS;
}
The SPDX-License-Identifier is a common way to indicate the license of the code. I use CC0-1.0, which basically means "use as you wish, just don't blame the author for any issues: no guarantees, no warranties."
The #define _POSIX_C_SOURCE 200809L tells the GNU C library that we want it to expose POSIX.1-2008 features, which include getline(). If you look at man 3 getline, you'll see in the Synopsis section that glibc 2.10 and later require _POSIX_C_SOURCE to be defined to at least 200809L.
Most of the code is to print the usage, and getting the source and target file names from the command line, and handling - as a special name, "standard stream", so that it can be used even in pipes by specifying - as the input and/or output file name.
The getline() loop uses fwrite() to write the line to the target file. This way, if the input contains embedded NUL bytes (\0), the target will still be identical to the source file.
After the loop, we discard the line buffer, although since the program is just about to exit, we could omit that (since the OS will release all dynamically allocated (non-shared) memory when we exit anyway).
I like code that checks with ferror(src) || !feof(src) if an error occurred in src or src did not reach end of input; and that checks the return value of fclose(), in case a delayed (write) error is reported. Granted, fclose() should never fail for a read-only file, and fclose() should only fail for files we've written to in specific circumstances, but it costs very little to check, and this way the user running the program will be told if the program detected loss of data.
I believe it is morally reprehensible to ignore checking for such errors (especially "because they occur so rarely"), since such tests are the only way the human user can know whether the operation was successful, or if some odd problem occurred. It is up to the human to investigate any problems, and up to our programs to report detectable issues.
The getline function takes a FILE * as a parameter, not an int. Replace the following line:
int fd = open("./rules.txt", O_RDONLY);
By;
FILE *fin = fopen("./rules.txt", "r");
Fix the error checking in the following lines accordingly, like you did with fout.
Then replace the line:
int bytesRead = getline(&line, &len, fd);
Instead it should now use fin:
ssize_t bytesRead = getline(&line, &len, fin);
Note that getline returns ssize_t, not int.
You are also never writing to fout, but I guess you're still working on this code.
Make sure to enable compiler warnings, because your compiler would surely have warned you for using an int parameter where a FILE * was expected.

Opening a file using relative path

The following code is supposed to work as follows: print the list of the files in a directory, and print the content of each .c file.
it works fine when executed in UNIX for the same directory: ./a.out ./
However, I was not able to make it work for ./a.out ../differentDir execution.
I know that if the absolute path is provided as an argument, I could use argv[1] for that. However, when it is provided in a form of a relative path I am lost.
#include <sys/types.h>
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#define BUFFSIZE 32768
int main(int argc, char **argv) {
char buf[BUFFSIZE];
DIR *dp;
struct dirent *dirp;
char filename[80];
int name_length;
FILE *fp;
if (argc != 2) {
fprintf(stderr, "usage: %s dir_name\n", argv[0]);
exit(1);
}
if ((dp = opendir(argv[1])) == NULL ) {
fprintf(stderr, "can't open '%s'\n", argv[1]);
exit(1);
}
while ((dirp = readdir(dp)) != NULL ){
printf("%s\n", dirp->d_name);
memset(filename, '\0', sizeof(filename));
strcpy(filename, dirp->d_name);
printf(" ** %s ", filename);
name_length = strlen(filename);
printf(" name_length=%d \n", name_length);
if (findC(filename)) // checking if the file has a .c extension
{
fp=fopen(filename, "r");
if (fp == NULL)
fprintf(stderr, "Can't open .C file!\n");
else
{// if the file was opened successfuly:
do
{
fgets(buf,BUFFSIZE,fp); // reading each line until buffer is full or until reaching whitespace
buf[strlen(buf)-1]='\0'; // removing the trailing whitespace from the buffer
puts(buf);
}
while (!feof(fp));
printf("\n\n");
fclose(fp);
}
}
}
closedir(dp);
return(0);
}
/*FindC method gets a c-string that represents a file name; returns 1 if the file ends with .C extension, else returns 0*/
int findC(char * name)
{
int len = strlen(name);
if (len>=2 && name[len-2]=='.' && tolower(name[len-1])=='c')
return 1;
return 0;
}
Upon opening the file to read, the file pathname needs to also be relative.
// Form prefix for complete relative file name
char filename[MAXPATH];
strcpy(filename, argv[1]);
// append '/' if directory path does not end in '/'
if (TBD_code(filename)) {
strcat(filename, "/");
}
char *end = filename[strlen(filename)];
while ((dirp = readdir(dp)) != NULL ){
printf("%s\n", dirp->d_name);
if (findC(dirp->d_name)) {
// append filename to prefix
strcpy(end, dirp->d_name);
fp=fopen(filename, "r");
...
You can use realpath(argv1...) like in this example. realpath will return the absolute path for a relative path.
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
int main(int argc, char **argv) {
char *path = "../..";
char buff[PATH_MAX + 1]; /* not sure about the "+ 1" */
char *res = realpath(path, buff);
if (res) {
printf("This source is at %s.\n", buff);
} else {
perror("realpath");
exit(EXIT_FAILURE);
}
return 0;
}
To include the desired behavior in your program, you can use realpathin your code:
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#include <ctype.h>
#include <dirent.h>
#include <string.h>
#define BUFFSIZE 32768
int main(int argc, char **argv) {
char buf[BUFFSIZE];
DIR *dp;
struct dirent *dirp;
char filename[80];
int name_length;
FILE *fp;
char buff[PATH_MAX + 1]; /* not sure about the "+ 1" */
if (argc != 2) {
fprintf(stderr, "usage: %s dir_name\n", argv[0]);
exit(1);
}
char *res = realpath(argv[1], buff);
if ((dp = opendir(res)) == NULL ) {
fprintf(stderr, "can't open '%s'\n", argv[1]);
exit(1);
}
while ((dirp = readdir(dp)) != NULL ){
printf("%s\n", dirp->d_name);
memset(filename, '\0', sizeof(filename));
strcpy(filename, dirp->d_name);
printf(" ** %s ", filename);
name_length = strlen(filename);
printf(" name_length=%d \n", name_length);
if (findC(filename)) // checking if the file has a .c extension
{
fp=fopen(filename, "r");
if (fp == NULL)
fprintf(stderr, "Can't open .C file!\n");
else
{// if the file was opened successfuly:
do
{
fgets(buf,BUFFSIZE,fp); // reading each line until buffer is full or until reaching whitespace
buf[strlen(buf)-1]='\0'; // removing the trailing whitespace from the buffer
puts(buf);
}
while (!feof(fp));
printf("\n\n");
fclose(fp);
}
}
}
closedir(dp);
return(0);
}
/*FindC method gets a c-string that represents a file name; returns 1 if the file ends with .C extension, else returns 0*/
int findC(char * name)
{
int len = strlen(name);
if (len>=2 && name[len-2]=='.' && tolower(name[len-1])=='c')
return 1;
return 0;
}
You could first change to the directory chdir either with relative or absolute path and the get the absolute path via the getcwd
#include <sys/types.h>
#include <string.h>
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#define BUFFSIZE 32768
#define PATH_SIZE 512
int main(int argc, char **argv) {
char buf[BUFFSIZE];
char path[PATH_SIZE];
DIR *dp;
struct dirent *dirp;
char filename[80];
int name_length, r;
FILE *fp;
if (argc != 2) {
fprintf(stderr, "usage: %s dir_name\n", argv[0]);
exit(1);
}
strcpy(path, argv[1]);
r = chdir(path);
if( r != 0 )
{
printf("Invalid path '%s'\n",path);
exit(1);
}
getcwd(path,PATH_SIZE);
if ((dp = opendir(path)) == NULL ) {
fprintf(stderr, "can't open '%s'\n", argv[1]);
exit(1);
}
while ((dirp = readdir(dp)) != NULL ){
printf("%s\n", dirp->d_name);
memset(filename, '\0', sizeof(filename));
strcpy(filename, dirp->d_name);
printf(" ** %s ", filename);
name_length = strlen(filename);
printf(" name_length=%d \n", name_length);
if (findC(filename)) // checking if the file has a .c extension
{
fp=fopen(filename, "r");
if (fp == NULL)
fprintf(stderr, "Can't open .C file!\n");
else
{// if the file was opened successfuly:
do
{
fgets(buf,BUFFSIZE,fp); // reading each line until buffer is full or until reaching whitespace
buf[strlen(buf)-1]='\0'; // removing the trailing whitespace from the buffer
puts(buf);
}
while (!feof(fp));
printf("\n\n");
fclose(fp);
}
}
}
closedir(dp);
return(0);
}
/*FindC method gets a c-string that represents a file name; returns 1 if the file ends with .C extension, else returns 0*/
int findC(char * name)
{
int len = strlen(name);
if (len>=2 && name[len-2]=='.' && tolower(name[len-1])=='c')
return 1;
return 0;
}

Error validating the contents of a file using regex in C

I am having a problem with the below code validating a file using regex. My file must only contain letters or numbers. My regular expression is:
#define to_find "^[a-zA-Z0-9]+$"
which is located in my main.h file. The below code is in my main.c
#include <ctype.h>
#include <errno.h>
#include <regex.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include "main.h"
int main(int argc, char * argv[])
{
int ret_val;
regex_t regex;
FILE *fp;
char line[1024];
if (regcomp(&regex, to_find, REG_EXTENDED) != 0)
{
fprintf(stderr, "Failed to compile regex '%s'\n", to_find);
return EXIT_FAILURE;
}
if (argc > 2)
{
printf("Usage: tree OR tree [filename]\n");
return EXIT_FAILURE;
}
else if (argc == 2)
{
fp = fopen(strcat(argv[1],".dat"), "r");
printf("file opened\n");
while ((fgets(line, 1024, fp)) != NULL)
{
line[strlen(line) - 1] = '\0';
if ((ret_val = regexec(&regex, line, 0, NULL, 0)) != 0);
{
printf("Error: %s\n", line);
return EXIT_FAILURE;
}
}
fclose(fp);
printf("File closed\n");
}
return 0;
}
My file I am reading is called names.dat and contains:
int
char
[
double
What is happening is it is kicking out at the very first line which it should kick out at the 3rd line. I am sure this is pretty simple to solve but it seems I have not figured it out. I would appreciate any help. Also, how do I deal with the
\n
character in the file? this file will have several lines. Thanks in advance.
You have some small errors but the one that cause the error is:
// Do you see this sweet little semicolon :P ----------------+
if ((ret_val = regexec(&regex, line, 0, NULL, 0)) != 0); // <+
{
printf("Error: %s\n", line);
return EXIT_FAILURE;
}
beside this line:
fp = fopen(strcat(argv[1],".dat"), "r");
You cannot add to argv, you need to create a new buffer to hold the data, create a buffer with PATH_MAX size add append the path to it. Here an improved version:
#include <ctype.h>
#include <errno.h>
#include <regex.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <limits.h>
#define to_find "^[a-zA-Z0-9]+$"
int main(int argc, char * argv[])
{
int ret_val;
regex_t regex;
FILE *fp;
char file[PATH_MAX];
char line[1024];
if (regcomp(&regex, to_find, REG_EXTENDED) != 0)
{
fprintf(stderr, "Failed to compile regex '%s'\n", to_find);
return EXIT_FAILURE;
}
if (argc > 2)
{
printf("Usage: tree OR tree [filename]\n");
return EXIT_FAILURE;
}
else if (argc == 2)
{
sprintf(file, "%s.dat", argv[1]);
fp = fopen(file, "r");
if( fp == NULL ) {
perror("Error");
return -1;
}
printf("file opened\n");
while (fscanf(fp, "%1023s", line) > 0)
{
if ((ret_val = regexec(&regex, line, 0, NULL, 0)) != 0)
{
printf("Not match: %s\n", line);
//return EXIT_FAILURE;
} else {
printf("Match: %s\n", line);
}
}
regfree(&regex);
fclose(fp);
printf("File closed\n");
}
return 0;
}
See the diff: http://www.diffchecker.com/8itbz5dy
test:
$ gcc -Wall sample.c
$
$ cat name.dat
int
char
[
double
$ ./a.out name
file opened
Match: int
Match: char
Not match: [
Match: double
File closed
$

Displaying standard error messages

I am just testing a small program that I want to test.
I am wondering if there is a way to use the stderr to display what the actual error was.
For example, if the file doesn't exist. Is there a standard error that I can display.
I am using stderr, and I thought by using that, I could display what the actual error was.
For example. If the file doesn't exit. Does any errors get sent to stderr that can be displayed?
I hope I am clear with my question.
Many thanks for any advice.
#include <stdio.h>
#include <string.h>
int main(void)
{
char buffer[100] = {'\0'}; /* declare and clean buffer */
FILE *fp;
int len_of_buff = 0;
fp = fopen("licenseURL.txt", "r");
if(fp == NULL)
{
fprintf(stderr, "There was a error opening a file ???");
exit(1);
}
fgets(buffer, sizeof(buffer), fp);
len_of_buff = strlen(buffer);
buffer[len_of_buff + 1] = '\0'; /* null terminate */
printf("The url is: [ %s ]\n", buffer);
fclose(fp);
}
Replace your fprintf(stderr, ...) call with:
perror("file open");
(stderr is just a stream for sending error messages to, so that they don't get mixed up with the normal program output - in case you're redirecting to a file or similar).
Use the strerror() function to retrieve a string describing the error.
My untested version would look like this:
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static void
die(const char *errstr, ...) {
va_list ap;
va_start(ap, errstr);
vfprintf(stderr, errstr, ap);
va_end(ap);
exit(EXIT_FAILURE);
}
int
main(int argc, char **argv) {
static const char licenseURL[] = "licenseURL.txt";
static char buf[100]; /* declare a clean buffer */
FILE *fp;
size_t len = 0;
if(!(fp = fopen(licenseURL, "r")))
die("couldn't %s: %s\n", licenseURL, strerror(errno));
if(!fgets(buf, sizeof buf, fp))
die("fgets failed: %s\n", strerror(errno));
len = strlen(buf);
if(len > 1 && buf[len - 1] == '\n')
buf[len - 1] = '\0'; /* cut off trailing \n */
printf("The url is: [ %s ]\n", buf);
fclose(fp);
return 0;
}

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