Ok so i am writing a C program. The program is simple enough, when i run the program i give it a few parameter Ex ./proj1 cat hat bat, so then it asks me to input a list of words the program gives counts of how many times "cat", "hat", and "bat" occurs in that list.
I have the program working great.
Example
./pro1 cat hat bat
cat
.
(the program recognized a "." as the end of input)
Result:
cat:1
hat:0
bat:0
ok so my program runs perfectly in every test case i can think of, but I have to pass a series of tests that my professor has mas made.
here is the code of that test.
char *args[] = {"./main", "cat", "hat","bat",NULL};
char *result[] = {"Looking for 3 words\n",
"Result:\n",
"cat:1\n",
"hat:0\n",
"bat:0\n"};
FILE *out;
FILE *test;
test=fopen("test","w");
int i;
char *buffer=malloc(100*sizeof(char));
out = fopen("smp0.in", "w");
fprintf(out, "cat\n");
fprintf(out, ".\n");
fclose(out);
freopen("smp0.in", "r", stdin);
freopen("smp0.out", "w", stdout);
quit_if(main(4, args) != EXIT_SUCCESS);
fclose(stdin);
fclose(stdout);
out = fopen("smp0.out", "r");
for (i = 0; i < 5; i++) {
quit_if(fgets(buffer, 100, out) == NULL);
quit_if(strcmp(buffer, result[i]));
}
fclose(out);
return EXIT_SUCCESS;
}
ok so sending the quit_if() is the method that makes it fail. specifically
quit_if(strcmp(buffer, result[i]));
My output when i run the program is exactly as described. But between freopen() diverting stdout to a file and then reading it back it has changed somehow.
Result:
cat:1
hat:0
batÿ:0
is what the output becomes, but it is not like that before the file write and read, and for some reason it is always that weird y character.
any advice would be greatly appreciated.
Sorry for not posting more code but it's because it is a school project.
I am confident that it is the test that is wrong in some way and not my code, fixing the test is part of the project as well.
See this answer to a previous question:
https://stackoverflow.com/a/4906442/2009431
It seems that when the dot is read back in from your stdin file, it has an EOF token appended (makes sense) that would not normally be part of the user's input. Then, somehow (not sure since we can't see your code) your main() function is appending that EOF character onto "bat" in the form of that weird y character (see linked answer for details on why).
If I'm right, maybe this could be considered a bug in the test?
Related
It may be a stupid issue but its been a few hours I've been looking around to fix that and it drives me crazy.
That little code works perfectly fine if the fgets line is commentated (as provided).
As soon as I remove the comment the whole function will NOT do anything at all. My process jut freezes - even the printf before the fgets isnt executed.
void RetirerTransaction(char* filePath, char* transaction) {
FILE* f;
FILE* result;
char tempStr[128];
char line[100];
printf(">>%s<<",filePath); // Just to check everything is ok
strcpy(tempStr,"grep -v \"");
strcat(tempStr,transaction);
strcat(tempStr,"\"");
strcat(tempStr,filePath); // tempStr = grep -v "XXX" myfile
result = popen(tempStr, "r");
/*
if (fgets(line,100,result)) {
printf("OK");
}
*/
}
Thank you in advance.
You miss a space between the closing quote of the pattern and the file parameter for grep. That makes the whole thing including the filename be taken as the pattern.
By default, grep reads from standard input. It blocks trying to read from stdin because it doesn't have a file parameter.
Add the space like this and you'll be fine:
strcat(tempStr,"\" ");
Check the code below.Please add check for the popen return value. If popen fails and you are trying to do a fgets() then it might cause crash.
result = popen(tempStr, "r");
if(result == NULL)
return;
else
fgets(line,100,result);
I am working on a school project in which we have to do some operations (select, min, max) on a table saved in .txt file.
The problem is that we can't use common functions such as fopen, fscanf, fclose.
The program will be launched from command line like this: .\project.exe select parameters <table.txt
Do you have some ideas how to get content of the .txt file to stdin without using fopen?
Thanks.
You do not need to open the file - the operating environment will do it for you.
When your program is called with <table.txt, your standard input is switched to read from that file instead of the keyboard. You can use scanf to read the data, and do not worry about opening and closing the file.
Same goes for the output of your program and the >table_out.txt redirection: rather than printing to the screen, printfs in your program would be writing to a file, which would be automatically closed upon your program's exit. Of course if you need to print something to the screen when your output is redirected, you can do so by printing to stderr (e.g. fprintf(stderr, "Invalid table format\n").
There are few ways to acomplish this.
Reading STDIN
I guess the teacher wants this method in particular. The idea is reading standard input rather than particular file.
In C++ you can simply read the stdin object. Here's an example:
#include <stdio.h>
#include <string.h>
int main(void)
{
char str[80];
int i;
printf("Enter a string: ");
fgets(str, 10, stdin);
/* remove newline, if present */
i = strlen(str)-1;
if( str[ i ] == '\n')
str[i] = '\0';
printf("This is your string: %s", str);
return 0;
}
Source: http://www.java2s.com/Code/C/Console/Usefgetstoreadstringfromstandardinput.htm
Using system utils
You can call "type" util # Windows (not sure about it) or "cat" util in Linux as a subprocess to read some partticular file. But this is rather a "hack", so I do not recommend using this one.
I'm trying to recreate a program I saw in class.
The teacher made a file with 10 lines, he showed us that the file was indeed created, and then he displayed its contents.
My code doesn't work for some reason, it just prints what looks like a"=" a million times and then exits.
My code:
void main()
{
FILE* f1;
char c;
int i;
f1=fopen("Essay 4.txt","w");
for(i=0;i<10;i++)
fprintf(f1," This essay deserves a 100!\n");
do
{
c=getc(f1);
putchar(c);
}while(c!=EOF);
}
What is the problem? as far as I can see I did exactly what was in the example given.
The flow is as such:
You create a file (reset it to an empty file if it exists). That's what the "w" mode does.
Then you write stuff. Note that the file position is always considered to be at the very end, as writing moves the file position.
Now you try to read from the end. The very first thing you read would be an EOF already. Indeed, when I try your program on my Mac, I just get a single strange character just as one would expect from the fact that you're using a do { } while. I suggest you instead do something like: for (c = getc(f1); c != EOF; c = getc(f1)) { putchar(c) } or similar loop.
But also, your reading should fail anyway because the file mode is "w" (write only) instead of "w+".
So you need to do two things:
Use file mode "w+".
Reset the file position to the beginning of the file after writing to it: fseek(f1, 0, SEEK_SET);.
A friend of mine needs to use MATLAB for one of his classes, so he called me up (a Computer Science Major) and asked if I could teach him C. I am familiar with C++, so I am also familiar with the general syntax, but had to read up on the IO library for C.
I was creating some simple IO programs to show my friend, but my third program is causing me trouble. When I run the program on my machine using Eclipse (with the CDT) Eclipse's console produces a glitchy output where instead of prompting me for the data, it gets the input and then prints it all at once with FAILURE.
The program is supposed to get a filename from user, create the file, and write to it until the user enters a blank line.
When I compile/run it on my machine via console (g++ files2.c) I am prompted for the data properly, but FAILURE shows up, and there is no output file.
I think the error lies with how I am using the char arrays, since using scanf to get the filename will create a functional file (probably since it ignores whitespace), but not enter the while loop.
#include <stdio.h>
#define name_length 20
#define line_size 80
int main() {
FILE * write_file; // pointer to file you will write to
char filename[name_length]; // variable to hold the name of file
char string_buffer[line_size]; // buffer to hold your text
printf("Filename: "); // prompt for filename
fgets(filename, name_length, stdin); // get filename from user
if (filename[name_length-1] == '\n') // if last char in stream is newline,
{filename[name_length-1] = '\0';} // remove it
write_file = fopen(filename, "w"); // create/overwrite file user named
if (!write_file) {printf("FAILURE");} // failed to create FILE *
// inform user how to exit
printf("To exit, enter a blank line (no spaces)\n");
// while getting input, print to file
while (fgets(string_buffer, line_size, stdin) != NULL) {
fputs(string_buffer, write_file);
if (string_buffer[0] == '\n') {break;}
}
fclose(write_file);
return 0;
}
How should I go about fixing the program? I have found next to nothing on user-terminated input being written to file.
Now if you will excuse me, I have a couple of files to delete off of my University's UNIX server, and I cannot specify them by name since they were created with convoluted filenames...
EDIT------
Like I said, I was able to use
scanf("%s", filename);
to get a working filename (without the newline char). But regardless of if I use scanf or fgets for my while loop, if I use them in conjunction with scanf for the filename, I am not able to write anything to file, as it does not enter the while loop.
How should I restructure my writing to file and my while loop?
Your check for the newline is wrong; you're looking at the last character in filename but it may be before that if the user enters a filename that's shorter than the maximum. You're then trying to open a file that has a newline in it's name.
These lines seem to be incorrect:
if (filename[name_length-1] == '\n') // if last char in stream is newline,
{filename[name_length-1] = '\0';} // remove it
You verify the name_length - 1 character,, which is 19 in your case without any regard of the introduced filename's length. So if your file name's length is less then 18 you won't replace the '\n' character at the end of your string. Obviously the file name can't contain '\n' character.
You need to get the size of you file name first with strlen() as an example.
if (filename[strlen(filename) - 1] == '\n')
{
filename[strlen(filename) - 1] = '\0';
}
(Don't forget to include the string.h header)
I hope I was able to help with my weak english.
I am trying to create a a program that does the following actions:
Open a file and read one line.
Open another file and read another line.
Compare the two lines and print a message.
This is my code:
#include <stdio.h>
#include <string.h>
int findWord(char sizeLineInput2[512]);
int main()
{
FILE*cfPtr2,*cfPtr1;
int i;
char sizeLineInput1[512],sizeLineInput2[512];
cfPtr2=fopen("mike2.txt","r");
// I open the first file
while (fgets(sizeLineInput2, 512, cfPtr2)!=NULL)
// I read from the first 1 file one line
{
if (sizeLineInput2[strlen(sizeLineInput2)-1]=='\n')
sizeLineInput2[strlen(sizeLineInput2)-1]='\0';
printf("%s \n",sizeLineInput2);
i=findWord(sizeLineInput2);
//I call the procedure that compares the two lines
}
getchar();
return 0;
}
int findWord(char sizeLineInput2[512])
{
int x;
char sizeLineInput1[512];
File *cfPtr1;
cfPtr1=fopen("mike1.txt","r");
// here I open the second file
while (fgets(sizeLineInput1, 512,cfPtr1)!=NULL)
{
if (sizeLineInput1[strlen(sizeLineInput1)-1]=='\n')
sizeLineInput1[strlen(sizeLineInput1)-1]='\0';
if (strcmp(sizeLineInput1,sizeLineInput2)==0)
//Here, I compare the two lines
printf("the words %s and %s are equal!\n",sizeLineInput1,sizeLineInput2);
else
printf("the words %s and %s are not equal!\n",sizeLineInput1,sizeLineInput2);
}
fclose(cfPtr1);
return 0;
}
It seems to have some problem with file pointers handling. Could someone check it and tell me what corrections I have to do?
Deconstruction and Reconstruction
The current code structure is, to be polite about it, cock-eyed.
You should open the files in the same function - probably main(). There should be two parallel blocks of code. In fact, ideally, you'd do your opening and error handling in a function so that main() simply contains:
FILE *cfPtr1 = file_open("mike1.txt");
FILE *cfPtr2 = file_open("mike2.txt");
If control returns to main(), the files are open, ready for use.
You then need to read a line from each file - in main() again. If either file does not contain a line, then you can bail out with an appropriate error:
if (fgets(buffer1, sizeof(buffer1), cfPtr1) == 0)
...error: failed to read file1...
if (fgets(buffer2, sizeof(buffer2), cfPtr2) == 0)
...error: failed to read file2...
Then you call you comparison code with the two lines:
findWord(buffer1, buffer2);
You need to carefully segregate the I/O operations from the actual processing of data; if you interleave them as in your first attempt, it makes everything very messy. I/O tends to be messy, simply because you have error conditions to deal with - that's why I shunted the open operation into a separate function (doubly so since you need to do it twice).
You could decide to wrap the fgets() call and error handling up in a function, too:
const char *file1 = "mike1.txt";
const char *file2 = "mike2.txt";
read_line(cfPtr1, file1, buffer1, sizeof(buffer1));
read_line(cfPtr2, file2, buffer2, sizeof(buffer2));
That function can trim the newline off the end of the string and deal with anything else that you want it to do - and report an accurate error, including the file name, if anything goes wrong. Clearly, with the variables 'file1' and 'file2' on hand, you'd use those instead of literal strings in the file_open() calls. Note, too, that making them into variables means it is trivial to take the file names from the command line; you simply set 'file1' and 'file2' to point to the argument list instead of the hard-wired defaults. (I actually wrote: const char file1[] = "mike1.txt"; briefly - but then realized that if you handle the file names via the command line, then you need pointers, not arrays.)
Also, if you open a file, you should close the file too. Granted, if your program exits, the o/s cleans up behind you, but it is a good discipline to get into. One reason is that not every program exits (think of the daemons running services on your computer). Another is that you quite often use a resource (file, in the current discussion) briefly and do not need it again. You should not hold resources in your program for longer than you need them.
Philosophy
Polya, in his 1957 book "How To Solve It", has a dictum:
Try to treat symmetrically what is symmetrical, and do not destroy wantonly any natural symmetry.
That is as valid advice in programming as it is in mathematics. And in their classic 1978 book 'The Elements of Programming Style', Kernighan and Plauger make the telling statements:
[The] subroutine call permits us to summarize the irregularities in the argument list [...]
The subroutine itself summarizes the regularities of the code.
In more modern books such as 'The Pragmatic Programmer' by Hunt & Thomas (1999), the dictum is translated into a snappy TLA:
DRY - Don't Repeat Yourself.
If you find your code doing the 'same' lines of code repeated several times, write a subroutine to do it once and call the subroutine several times.
That is what my suggested rewrite is aiming at.
In both main() and findWord() you should not use strlen(sizeLineInputX) right after reading the file with fgets() - there may be no '\0' in sizeLineInput2 and you will have strlen() read beyond the 512 bytes you have.
Instead of using fgets use fgetc to read char by char and check for a newline character (and for EOF too).
UPD to your UPD: you compare each line of mike2.txt with each line of mike1.txt - i guess that's not what you want. Open both files one outside while loop in main(), use one loop for both files and check for newline and EOF on both of them in that loop.