Im trying to print the first line from each file, then the second line from each file and so on.
When getline = EOF, then that file is closed and filesAreOpen is decremented, though the program loops forever
void PrintLines(ifstream files[], size_t count)
{
string s;
ifstream *end, *start;
int filesAreOpen = count;
//continue while filesAreOpen > 0
while(filesAreOpen)
{
}
}
Actually you don't have to close files if EOF is reached. That will make your code much slower and painful to manage. Because you have to check if it is open, which involves file names. In this case, files are already open and you will read first line from each file than second line from each file and so on. But if a file reaches EOF, then of course you will miss that file and continue to read lines from other files. Until all files are reached EOF. Then close them all.
void PrintLines(ifstream files[], size_t count)
{
int filesAreOpen = count;
char line[250];
//continue while filesAreOpen > 0
while(filesAreOpen)
{
for(int i=0; i<count; i++)
{
if (!infile[i].eof())
{
infile[i].getline(line,250);
cout << line;
}
else
filesAreOpen--;
}
}
for(int i=0; i<count; i++)
files[i].close();
}
Related
I have made a program for my Arduino which will sort an array of fifty random numbers in ascending or descending order, I think I have got it all right, but when I run it I get an error message "expected unqualified-id before 'for' ".
int array [50];
int i = 0;
void setup() {
Serial.begin(9600); // Load Serial Port
}
void loop() {
// put your main code here, to run repeatedly:
Serial.println ("Position " + array[i]);
delay (2000);
}
for (i <= 50) { <-----*Here is where the error highlights*--->
int n = random (251); // Random number from 0 to 250
array[i] = n;
i++;
}
// Bubble sort function
void sort (int a[], int size) {
for(int i=0; i<(size-1); i++) {
for(int o=0; o<(size-(i+1)); o++) {
if(a[o] > a[o+1]) {
int t = a[o];
a[o] = a[o+1];
a[o+1] = t;
}
}
}
}
I have annotated where the error is shown. I need to get past this to test my code, I have no clue on how to fix it!
You have written it wrong. There is pseudocode of for loop:
for(datatype variableName = initialValue; condition; operation){
//your in loop code
}
//Code wich will be executed after end of for loop above
In your case it will look like this:
for(int i = 0; i < 50 ; i++){
int n = random (251); // Random number from 0 to 250
array[i] = n;
}
Another thing is, that you are trying to iterate the array. The first index is 0. It means the last index is 49 not 50. If you try to access 50th index it will crash your program.
Last thing is, that the for loop we are talking about is out of any method. It will never be executed.
The for loop requires three parts to its parameters:
A variable to count iterations
A condition that must be true to continure
A increment factor
Each part should be separated by a semicolon
So your for loop should start out like this:
for(int i = 0;i <= 50; i++){
//code here
}
Official arduino For Loop Reference
I am storing some data in QDataStream and immediately taking the data, but the count is showing zero while retriving. code looks fine but unexpected behaviour
//Overloading
QDataStream& operator<< (QDataStream& writeTO, const CascadeJobInfo& data)
{
writeTO << data.m_infoJobType << data.m_connectionName << data.m_submitJobId << data.m_submitJobStat;
return writeTO;
}
QDataStream& operator>> (QDataStream& readIn, CascadeJobInfo& data)
{
readIn >> data.m_infoJobType >> data.m_connectionName >> data.m_submitJobId >> data.m_submitJobStat;
return readIn;
}
void Fun()
{
// Code Starts here
projectFileName = /*Path to folder*/
QFile file(projectFileName);
file.open(QFile::ReadWrite);
file.close();
QDataStream dStream(&file);
int jobLstCount = /*Get the Count, assume 4*/
dStream << jobLstCount;
for(int i = 0; i < jobLstCount; i++)
{
JobInfo.m_infoJobType = jobFlowItem->getJobType();
JobInfo.m_connectionName = submitItem->connectionName();
JobInfo.m_submitJobId = submitItem->jobID();
JobInfo.m_submitJobStat = submitItem->jobState();
// All valid data stored here
}
file.close();
QDataStream dStreamOut(&file);
dStreamOut >> jobLstCount; /*Count returns zero here insted of 4*/
CascadeJobInfo jobInfo;
// Why jobLstCount is getting zero here
for(int i = 0 ; i < jobLstCount ; i++)
{
dStreamOut >> jobInfo;
}
}
file.open(QFile::ReadWrite);
file.close(); <--- HERE
QDataStream dStream(&file);
You are closing the file as soon as you open it, so basically you are working with an invalid file descriptor which won't work. Put file.close() at the end of the code when you are done.
I have recently started programming in UNIX environment. I need to write a program which creates an empty file with name and size given in the terminal using this commands
gcc foo.c -o foo.o
./foo.o result.txt 1000
Here result.txt means the name of the newly created file, and 1000 means the size of the file in bytes.
I know for sure that lseek function moves the file offset, but the trouble is that whenever I run the program it creates a file with a given name, however the size of the file is 0.
Here is the code of my small program.
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>
int main(int argc, char **argv)
{
int fd;
char *file_name;
off_t bytes;
mode_t mode;
if (argc < 3)
{
perror("There is not enough command-line arguments.");
//return 1;
}
file_name = argv[1];
bytes = atoi(argv[2]);
mode = S_IWUSR | S_IWGRP | S_IWOTH;
if ((fd = creat(file_name, mode)) < 0)
{
perror("File creation error.");
//return 1;
}
if (lseek(fd, bytes, SEEK_SET) == -1)
{
perror("Lseek function error.");
//return 1;
}
close(fd);
return 0;
}
If you aren't allowed to use any other functions to assist in creating a "blank" text file, why not change your file mode on creat() then loop-and-write:
int fd = creat(file_name, 0666);
for (int i=0; i < bytes; i++) {
int wbytes = write(fd, " ", 1);
if (wbytes < 0) {
perror("write error")
return 1;
}
}
You'll want to have some additional checks here but, that would be the general idea.
I don't know whats acceptable in your situation but, possibly adding just the write() call after lseek() even:
// XXX edit to include write
if ((fd = creat(file_name, 0666)) < 0) {
perror("File creation error");
//return 1;
}
// XXX seek to bytes - 1
if (lseek(fd, bytes - 1, SEEK_SET) == -1) {
perror("lseek() error");
//return 1;
}
// add this call to write a single byte # position set by lseek
if (write(fd, " ", 1) == -1) {
perror("write() error");
//return 1;
}
close(fd);
return 0;
I am writing a data logger and would like to keep the files limited to a specific number of entries. I am trying to write this bit of code in the setup, so that when the Arduino powers on, it will write to a new file just to keep things simple. However, when I try to open the file I can't, although I am not sure why. Can anyone offer any explanation?
char *fileName; //global name
File logFile; //global file
//everything else is in setup()
char * topPart = "/Data/Data"; //first part of every file
char * lowerPart = ".txt"; // jus the extention
char * itter; //used to hold the char of i later
fileName = "/Data/Data.txt"; //start with the first file possible.
for(int i=0; i<=100;i++) {
if(!SD.exists(fileName)) {
Serial.print("opening file: ");
Serial.print(fileName);
logFile = SD.open(fileName, FILE_WRITE);
if(logFile) {
logFile.println("I made it");
Serial.println("in the file");
}
if(!logFile) {
Serial.println("somthing bad");
}
break;
} else {
itter = (char *)(i+48);
strcpy(fileName,topPart);
strcpy(fileName,itter);
strcpy(fileName,lowerPart);
Serial.println(i);
}
}
Lots of problems.
the construction of itter is wrong.
strcpy doesn't append just cpy.
Here is a code example to build your filename. This a basic C program. Remove the #include and main for Arduino, this allows to test on your computer whether the program is ok.
#include <string.h>
#define TOPPART "/Data/Data"
#define LOWERPART ".txt"
int main(void) {
char buf[64];
snprintf(buf, sizeof(buf), "%s%s", TOPPART, LOWERPART);
for (int i = 0; i < 100; i++) {
/* here your stuff to check if the filename froml buf exists*/
snprintf(buf, sizeof(buf), "%s%d%s", TOPPART, i, LOWERPART);
}
return 0;
}
Pointer related question. I'm going through some example code that currently reads in data from a file called dataFile into a buffer. The reading is done inside a loop as follows:
unsigned char* buffer = (unsigned char*)malloc(1024*768*);
fread(buffer,1,1024*768,dataFile);
redPointer = buffer;
bluePointer = buffer+1024;
greenPointer = buffer+768;
Now, I want to try and write the entire contents of the array buffer to a file, so that I can save just those discrete images (and not have a large file). However, I am not entirely sure how to go about doing this.
I was trying to cout statements, however I get a print-out of garbage characters on the console and also a beep from the PC. So then I end my program.
Is there an alternative method other than this:
for (int i=0; i < (1024*768); i++) {
fprintf(myFile, "%6.4f , ", buffer[i]);
}
By declaring your buffer as a char*, any pointer arithmatic or array indexes will use sizeof(char) to calculate the offset. A char is 1 byte (8 bits).
I'm not sure what you are trying to do with the data in your buffer. Here are some ideas:
Print the value of each byte in decimal, encoded as ASCII text:
for (int i=0; i < (1024*768); i++) {
fprintf(myFile, "%d , ", buffer[i]);
}
Print the value of each byte in hexadecimal, encoded in ASCII text:
for (int i=0; i < (1024*768); i++) {
fprintf(myFile, "%x , ", buffer[i]);
}
Print the value of each floating point number, in decimal, encoded in ASCII text (I think my calculation of the array index is correct to process adjacent non-overlapping memory locations for each float):
for (int i=0; i < (1024*768); i += sizeof(float)) {
fprintf(myFile, "%6.4f , ", buffer[i]);
}
Split the buffer into three files, each one from a non-overlapping section of the buffer:
fwrite(redPointer, sizeof(char), 768, file1);
fwrite(greenPointer, sizeof(char), 1024-768, file2);
fwrite(bluePointer, sizeof(char), (1024*768)-1024, file3);
Reference for fwrite. Note that for the count parameter I simply hard-coded the offsets that you had hard-coded in your question. One could also subtract certain of the pointers to calculate the number of bytes in each region. Note also that the contents of these three files will only be sensible if those are sensibly independent sections of the original data.
Maybe this gives you some ideas.
Updated: so I created a complete program to compile and test the formatting behavior. This only prints the first 20 items from the buffer. It compiles (with gcc -std=c99) and runs. I created the file /tmp/data using ghex and simply filled in some random data.
#include <stdlib.h>
#include <stdio.h>
int main()
{
FILE* dataFile = fopen("/tmp/data", "rb");
if (dataFile == NULL)
{
printf("fopen() failed");
return -2;
}
unsigned char* buffer = (unsigned char*)malloc(1024*768);
if (buffer == NULL)
{
printf("malloc failed");
return -1;
}
const int bytesRead = fread(buffer,1,1024*768,dataFile);
printf("fread() read %d bytes\n", bytesRead);
// release file handle
fclose(dataFile); dataFile = NULL;
printf("\nDecimal:\n");
for (int i=0; i < (1024*768); i++) {
printf("%hd , ", buffer[i]);
if (i > 20) { break; }
}
printf("\n");
printf("\nHexadecimal:\n");
for (int i=0; i < (1024*768); i++) {
printf("%#0hx , ", buffer[i]);
if (i > 20) { break; }
}
printf("\n");
printf("\nFloat:\n");
for (int i=0; i < (1024*768); i += sizeof(float)) {
printf("%6.4f , ", (float)buffer[i]);
if (i > 20) { break; }
}
printf("\n");
return 0;
}