I need help with reading instructions from a text file. So for example:
Let's say this is my text file:
a 38
s 20
a 10
s 10
'a' stands for add, 's' stands for subtract, and the number separated by a tab is the number I want to either add or subtract from a total. So I want my program to read this line by line and perform the operation specified.
Example: If my total starts at 0, I want the program to read "a tab 38" on the first line and add 38 to the total, and then move on to the next line and read "s tab 20" on the second line and subtract 20 from the total. So on and so forth.
I know how to get the program to read the file, but I'm not sure how to get it to recognize the a/s, the tab, and the number, and then keep doing it for each line.
Any help would be greatly appreciated because I'm really stuck.
use fscanf(yourfileptr, "%c\t%d", &instruction, &operand) to get the instruction and the operand. then you can simply add or subtract the operand according to the instruction character.
Maybe you can try this . Code I haven't checked properly but that should be the line of coding. This is inside main function code.
FILE *fp;
char buff[255];
char numBuff[10];
int a;
int val = 0;
char op;
int len;
fp = fopen("/tmp/test.txt", "r");
while(fgets(buff, 255, file) != NULL){
len = strlen(buff);
strncpy (numBuff, buff+2, len-2);
numBuff[len-2] = '\0';
a = atoi(numBuff);
if(buff[0] == 's'){
val -= a;
}else if(buff[0]=='a'){
val += a;
}
}
printf("%d",val);
Related
I'm currently trying to read some star data from the BSC. I've managed to read in the header and that shows up more or less correct, but I'm having trouble reading in the star data itself. The specification states that values are stored as 4/8-byte "Real" numbers, which I assumed meant floats/doubles, but the Ascension and Declination I get are all wrong, a good bit above the trillions for one and zero for the other. The magnitude is also wrong, despite it just being an integer, which I could read fine in the header. Here's and image of the output thus far. Any know what I'm doing wrong?
Alright, after some more testing, I managed to solve my problem. The crucial step was to abandon the binary file altogether and use the ASCII file instead. I had some problems reading from it before due to how it was formatted, but I came up with a method that worked:
/* Struct to store all the attributes I'm interested in */
struct StarData_t{
char Name[11];
char SpType[21];
float GLON, GLAT, Vmag;
};
int main()
{
/* Allocate a list of the structs
(the BSC has 9110 entries) */
struct StarData_t stars[9110];
/* Open the catalog */
FILE *fptr = fopen("catalog", "r");
if(fptr != NULL){
/* Create a buffer for storing the star entries.
The ASCII file has one entry per line.
Each line has a max length of 197,
which becomes 199 with the newline and null terminator,
so I round up to 200. */
size_t star_size = 200;
char *star_buffer;
star_buffer = (char *)malloc(star_size * sizeof(char));
/* Create a buffer for reading in the numbers.
The catalog has no numbers longer than 6 characters,
So I allocate 7 to account for the newline. */
char data_buffer[7];
/* For each entry in the BSC... */
for(int i = 0; i < 9110; i++){
/* Read the line to the buffer */
getline(&star_buffer, &star_size, fptr);
/* And put the data in the matching index,
Using the data buffer to create the floats */
// GLON
strncpy(data_buffer, &(star_buffer[90]), 6);
data_buffer[6] = '\0';
stars[i].GLON = fmod(atof(data_buffer)+180, 360)-180;
// GLAT
strncpy(data_buffer, &(star_buffer[96]), 6);
data_buffer[6] = '\0';
stars[i].GLAT = atof(data_buffer);
// Vmag
strncpy(data_buffer, &(star_buffer[102]), 5);
data_buffer[5] = '\0';
stars[i].Vmag = atof(data_buffer);
// Name
strncpy(stars[i].Name, &(star_buffer[4]), 10);
stars[i].Name[10] = '\0';
// Spectral Type
strncpy(stars[i].SpType, &(star_buffer[127]), 20);
stars[i].SpType[20] = '\0';
printf("Name: %s, Long: %7.2f, Lat: %6.2f, Vmag: %4.2f, SpType: %s\n", stars[i].Name, stars[i].GLON, stars[i].GLAT, stars[i].Vmag, stars[i].SpType);
}
free(star_buffer);
}
}
Hope this is useful!
I'm a beginner at C programming and I would appreciate some help in order to understand the problem.
Alright so, I have a data file (input.dat) with data like this: (first line) 0 2 3 4 5; (second line) 1 2 3 5 4, (third line and so on...). I'm required to read the data one line at a time until the end of file and print it. This is what I have done so far:
int main(void)
{
float coeffs[5];
FILE *input; /* File pointer to the input file */
fopen_s(&input, "input.dat", "r"); /* Location of the input file */
int count = 0;
/* Loops to read data set*/
while (fscanf_s(input, "%f %f %f %f %f ", &coeffs[0], &coeffs[1], &coeffs[2], &coeffs[3], &coeffs[4]) != EOF)
{
printf("a=%.4f; b=%.4f; c=%.4f; d=%.4f; e=%.4f\n", coeffs[0], coeffs[1], coeffs[2], coeffs[3], coeffs[4]);
count++;
}
return 0;
}
This is showing all of the lines in the data file at once. But this is not what I want. I need to read one line at a time and perform some calculations and conditions for that one line first before I move to the next line. So how can I do that?
Next problem is, for the first line, I need to implement a loop from -10 to +10 with increment of 2 (to get 11 results in total). For example the program will read the first line, display it on the screen, then for the first value -10, the program will calculate and again display something . Then it will do the same for -8, then for -6 and so on until +10. After the 11 results are displayed, the program will then and ONLY then, move to the second line and so on. Hence for each line in the data file, the program will have 11 results. How can I use the loop function with increment of 2 to achieve these 11 results?
I would appreciate if anyone can provide me a simple layout of the structure of the codes which I've to write. NOTE: The formats are a bit different than other compilers as I must use Microsoft Visual Studio to do it.
Add your calculations to your while loop. You are reading one line at a time anyway.
If you want to loop from -10 to 10 with increments of 2, use a for loop.
for(count = -10; count <= 10; count = count + 2)
{
// Calculations
}
I am quite rusty with C and system calls and pointers in general, so this is a good refresher exercise to get back on track. All I need to do is, given a file such as this:
YYY.txt: "somerandomcharacters"
Change it to be like this:
YYY.txt: "somerandomabcdefghijklmnopqrstuvwxyzcharacters"
So all that is done is some characters added to the middle of the file. Obviously, this is quite simple, but in C you must keep track and manage the size of the file in advance before adding the additional characters.
Here is my naive try:
//(Assume a file called YYY.txt exists and an int YYY is the file descriptor.)
char ToBeInserted[26] = "abcdefghijklmnopqrstuvwxyz";
//Determine the current length of YYY
int LengthOfYYY = lseek(YYY, 0, 2);
if(LengthOfYYY < 0)
printf("Error upon using lseek to get length of YYY");
//Assume we want to insert at position 900 in YYY.txt, and length of YYY is over 1000.
//1.] Keep track of all characters past position 900 in YYY and store in a char array.
lseek(YYY, 900, 0); //Seeks to position 900 in YYY, so reading begins there.
char NextChar;
char EverythingPast900[LengthOfYYY-900];
int i = 0;
while(i < (LengthOfYYY - 900)) {
int NextRead = read(YYY, NextChar, 1); //Puts next character from YYY in NextChar
EverythingPast900[i] = NextChar;
i++;
}
//2.] Overwrite what used to be at position 900 in YYY:
lseek(YYY, 900, 0); //Moves to position 900.
int WriteToYYY = write(YYY, ToBeInserted, sizeof(ToBeInserted));
if(WriteToYYY < 0)
printf("Error upon writing to YYY");
//3.] Move to position 900 + length of ToBeInserted, and write the characters that were saved.
lseek(YYY, 926, 0);
int WriteMoreToYYY = write(YYY, EverythingPast900, sizeof(EverythingPast900));
if (WriteMoreToYYY < 0) {
printf("Error writing the saved characters back into YYY.");
}
I think the logic is sound, mostly, although there are much better ways to do it in C. I need help on my C pointers, basically, as well as the UNIX system calls. Does anyone mind walking me through how to properly implement this in C?
That's the basic idea. If you had to really conserve RAM and the file was a lot bigger you'd want to copy block by block in reverse order. But the simpler way is to read the entire thing into memory and rewrite the entire file.
also, I prefer the stream functions: fopen, fseek, fread. But the file descriptor method works.
Hello I have file with text:
14
5 4
45 854
14
4
47 5
I need to write a text to a specific line. For example to the line number 4 (Doesn't matter whether I will append the text or rewrite the whole line):
14
5 4
45 854
14 new_text
4
47 5
I have found function fseek(). But in the documentation is written
fseek(file pointer,offset, position);
"Offset specifies the number of positions (bytes) to be moved from the location specified bt the position."
But I do not know the number of bites. I only know the number of lines. How to do that? Thank you
You can't do that, (text) files are not line-addressable.
Also, you can't insert data in the middle of a file.
The best way is to "spool" to a new file, i.e. read the input line by line, and write that to a new file which is the output. You can then easily keep track of which line you're on, and do whatever you want.
I will assume that you are going to be doing this many times for a single file, as such you would be better indexing the position of each newline char, for example you could use a function like this:
long *LinePosFind(int FileDes)
{
long * LinePosArr = malloc(500 * sizeof(long));
char TmpChar;
long LinesRead = 0;
long CharsRead = 0;
while(1 == read(FileDes, &TmpChar, 1))
{
if (!(LinesRead % 500)
{
LinePosArr = realloc(LinePosArr, (LinesRead + 500) * sizeof(long));
}
if (TmpChar == '\n')
{
LinePosArr[LinesRead++] = CharsRead;
}
CharsRead++;
}
return LinePosArr;
}
Then you can save the index of all the newlines for repeated use.
After this you can use it like so:
long *LineIndex = LinePosFind(FileDes);
long FourthLine = LineIndex[3];
Note I have not checked this code, just written from my head so it may need fixes, also, you should add some error checking for the malloc and read and realloc if you are using the code in production.
I am writing a c program that opens a txt file and want to read the last line of the txt file.
I am not that proficient in C so bear in mind that I may not know all of the concepts in C. I am stuck at the part where I use fscanf to read all the lines of my txt file but I want to take the last line of the txt file and get the values as described below.
Here is my incomplete code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
FILE *sync;
void check()
{
int success; //to hold the results if the timestamps match
sync = fopen("database.txt","r");
char file[] = "database.txt";
while (fscanf(sync, "%d.%06d", &file) != EOF)
{
}
fclose(sync);
}
sample txt file:
/////// / //// ///// ///// //////////////// Time: 1385144574.787665 //////// /
/////// / //// ///// ///// //////////////// Time: 1385144574.787727 //////// /
/////// / //// ///// ///// //////////////// Time: 1385144574.787738 //////// /
/////// / //// ///// ///// //////////////// Time: 1385144574.787746 //////// /
/////// / //// ///// ///// //////////////// Time: 1385144574.787753 //////// /
The / are some words, symbols and numbers I do not want, just the numbers in sample txt as shown above
I appreciate any examples and pointing out errors I made so I can understand this much better.
Since I made some people confused about the text file, here is what it really is. This is the format it will be so I should know the length of each line. However, I will not be able to know how many lines there will be as it may be updated.
Socket: 0 PGN: 65308 Data: 381f008300000000 Time: 1385144574.787925 Address: 28
Socket: 0 PGN: 65398 Data: 0000000100000000 Time: 1385144574.787932 Address: 118
Socket: 0 PGN: 61444 Data: f07d83351f00ffff Time: 1385144574.787940 Address: 4
Socket: 0 PGN: 65266 Data: 260000000000ffff Time: 1385144574.787947 Address: 242
Socket: 0 PGN: 65309 Data: 2600494678fff33c Time: 1385144574.787956 Address: 29
Socket: 0 PGN: 65398 Data: 0000000100000000 Time: 1385144574.787963 Address: 118
Socket: 0 PGN: 61444 Data: f07d833d1f00ffff Time: 1385144574.787971 Address: 4
Socket: 0 PGN: 65398 Data: 0000000100000000 Time: 1385144574.787978 Address: 118
Socket: 0 PGN: 61443 Data: d1000600ffffffff Time: 1385144574.787985 Address: 3
Socket: 0 PGN: 65308 Data: 451f008300000000 Time: 1385144574.787993 Address: 28
Socket: 0 PGN: 65317 Data: e703000000000000 Time: 1385144574.788001 Address: 37
Again I am after the Time values (eg. 1385144574.787925) at the last line of the txt file.
Hope this helps.
Since you're after the last line of the file, and you didn't mention how large the file might be, it could be worth while to start reading the file from the end, and work your way backwards from there:
FILE *fp = fopen("database.txt", "r");
fseek(fp, 0, SEEK_END);//sets fp to the very end of your file
From there, you can use fseek(fp, -x, SEEK_CUR); where x is the number of bytes you want to go back, until you get to where you want... other than that, Jekyll's answer should work just fine.
However, to get the last line, I tend to do something like this:
FILE *fp = fopen("database.txt", "r");
char line[1024] = "";
char c;
int len = 0;
if (fp == NULL) exit (EXIT_FAILURE);
fseek(fp, -1, SEEK_END);//next to last char, last is EOF
c = fgetc(fp);
while(c == '\n')//define macro EOL
{
fseek(fp, -2, SEEK_CUR);
c = fgetc(fp);
}
while(c != '\n')
{
fseek(fp, -2, SEEK_CUR);
++len;
c = fgetc(fp);
}
fseek(fp, 1, SEEK_CUR);
if (fgets(line, len, fp) != NULL) puts(line);
else printf("Error\n");
fclose(fp);
The reasoning behind my len var is so that I can allocate enough memory to accomodate the entire line. Using an array of 1024 chars should suffice, but if you want to play it safe:
char *line = NULL;
//read line
line = calloc(len+1, sizeof(char));
if (line == NULL)
{
fclose(fp);
exit( EXIT_FAILURE);
}
//add:
free(line);//this line!
fclose(fp);
Once you've gotten that line, you can use Jekyll's sscanf examples to determine the best way to extract whatever you want from that line.
The way you are using fscanf is wrong as the actual vector of arguments needs to match what you are collecting (as you can see in the manpage). Instead of using fscanf you may consider using fgets and then filtering for what you are looking for in the latest raw with a regex through sscanf.
Note:: I collected the value in double format, you may choose the format that suits you the most for your problem (string?int.int?float?), in order to do this you should check for regex using scanf. Please come back if you cannot accomplish this task.
update:: due to some requests I wrote some few examples of different pattern matching. These should be a good starting point to fix your problems.
update::
1. I have seen that you added the pattern of your db file so we can now state that both #3 and #4 match and put the 3 here (faster).
2. I removed the feof check as for your request, but note that the check is fine if you know what you are doing. Basically you have to keep in mind that stream's internal position indicator may point to the end-of-file for the next operation, but still, the end-of-file indicator may not be set until an operation attempts to read at that point.
3. You asked to remove the char line[1024]={0,}; This instruction is used to initialize the line[1024] array which will contain the lines that you read from the file. This is needed! To know what that instruction is please see here
Code:
void check()
{
char line[1024]={0,}; // Initialize memory! You have to do this (as for your question)
int n2=0;
int n3=0;
sync = fopen("database.txt", "r");
if( sync ) {
while( fgets(line, 1024, sync) !=NULL ) {
// Just search for the latest line, do nothing in the loop
}
printf("Last line %s\n", line); //<this is just a log... you can remove it
fclose(sync);
// This will look for Time and it will discard it collecting the number you are looking for in n2 and n3
if (sscanf(line, "%*[^T]Time: %d.%d", &n2, &n3) ) {
printf( "%d.%d\n", n2, n3);
}
}
}
Example 2
if for instance you need to collect the value using two integers you will need to replace the sscanf of the example above with the following code:
unsigned int n2, n3;
if (sscanf(line, "%*[^0-9]%d.%d", &n2, &n3) ) {
printf( "%d.%d\n", n2, n3);
}
said this you should figure out how to collect other formats.
Example 3
A better regex. In case there are others number in the file before the giving pattern you may want to match on Time, so let's say that there isn't any T before. A regex for this can be:
if (sscanf(line, "%*[^T]Time: %d.%d", &n2, &n3) ) {
printf( "%d.%d\n", n2, n3);
}
The regex using sscanf can be not suitable for your pattern, in that case you need to consider the usage of gnu regex library or you can mix strstr and sscanf like I did in the following example.
Example 4
This can be useful if you don't find a common pattern. In that case you may want to trigger on the string "Time" using strstr before calling the sscanf
char *ptr = strstr( line, "Time:" );
if( ptr != NULL ) {
if (sscanf(ptr, "%*[^0-9]%d.%d", &n2, &n3) ) {
printf( "%d.%d\n", n2, n3);
}
}
* Note *
You may need to find your way to parse the file and those above can be only suggestions because you may have more specific or different patterns in your file but the instruction I posted here should be enough to give you the instruments to do the job in that case