System Calls: Outputing file and pausing every 20 lines - c

Question

So I'm reading in files and outputting the contents of the files onto the console using system calls. Also I want to add a space to the output, every 20 lines I encounter. This is where I'm having trouble, in that despite the following few lines of code, the entire file is being displayed without the spaces
//Write file contenst
while( (nReadFile = read(nOpenFile, buffer, 1) != 0))
{
write(1, &nLineCount, sizeof(nLineCount));
if(nLineCount == 20)
{
write(1, "\n", 2);
nLineCount = 0;
}
if(nReadFile = write(1, buffer, nReadFile) == '\n')
{
nLineCount++;
}
}
Here is the entire program (Excluding the .h file containing the libraries)
#include"mymore.h"
int main(int argCount, char *argv[])
{
struct termios initial_settings, new_settings;
tcgetattr(fileno(stdin), &initial_settings);
new_settings=initial_settings;
new_settings.c_lflag &= ~ICANON;
new_settings.c_lflag &= ~ECHO;
new_settings.c_cc[VMIN] = 1;
new_settings.c_cc[VTIME] = 0;
if (tcsetattr(fileno(stdin), TCSANOW, &new_settings)!=0)
{
fprintf(stderr, "could not set attributes\n");
}
int nLineCount = 0;
int nCheckFile = 0;
int nFileCountCounter = 1; //first arguement interested in is argv[1]
int nOpenFile = 0;
int nReadFile = 0;
int nCount = 0;
char *cData;
char buffer[0];
//check that arguements have been provided
if( argCount < 2)
{
write(1, "There needs to be at least one file provided! \n", 50);
return 1;
}
do
{
printf("%d", argCount);
//check if file exists
nCheckFile = access(argv[nFileCountCounter], F_OK);
if(nCheckFile != 0) //if file does not exist
{
write(1, "The file ", 10);
write(1, argv[nFileCountCounter], strlen(argv[1]));
write(1," does not exist! \n", 25);
return 1;
}
else //file does exist
{
write(1, "Opening ", 10);
write(1, argv[nFileCountCounter], strlen(argv[1]));
write(1, "\n", 2);
}
//open the file
nOpenFile = open(argv[nFileCountCounter], O_RDONLY);
if(nOpenFile < 0)
{
write(1, "Failed to open file ", 10);
write(1, argv[nFileCountCounter], strlen(argv[nFileCountCounter]));
write(1, "\n", 2);
return 1;
}
//read file
cData = (char *) malloc(100 * sizeof(char));
cData[nReadFile] = '\0';//append null terminator
//find length of source file
while(cData[nCount] != 0)
{
nCount++;
}
//Write file contenst
while( (nReadFile = read(nOpenFile, buffer, 1) != 0))
{
write(1, &nLineCount, sizeof(nLineCount));
if(nLineCount == 20)
{
write(1, "\n", 2);
nLineCount = 0;
}
if(nReadFile = write(1, buffer, nReadFile) == '\n')
{
nLineCount++;
}
}
cout << nLineCount << endl;
//close file
close(nOpenFile);
//Increment to next file
nFileCountCounter++;
}while(nFileCountCounter < argCount);//while there are still arguements
tcsetattr(fileno(stdin), TCSANOW, &initial_settings);
return 0;
}
This is actually my first experience using system calls, and one thing I think I've noticed is that the write command is being executed before any of the c code?
Any ideas?
Thanks

Answer 1

There are plenty of mistakes in your code:
char buffer[0]; should be char buffer[1];
char buffer[0]; defines a buffer which can store zero character, I suppose it is not what you want.
write(1, "There needs to be at least one file provided! \n", 50); should be
char *msg = "There needs to be at least one file provided! \n";
write(1, msg, strlen(msg));
the message is longer than 50. There are serval similar mistakes, and can be fixed similarly.
while( (nReadFile = read(nOpenFile, buffer, 1) != 0)) should be
while( (nReadFile = read(nOpenFile, buffer, 1)) != 0)
In C, operator != has higher precedence than =, so nReadFile = read(nOpenFile, buffer, 1) != 0 meas nReadFile = (read(nOpenFile, buffer, 1) != 0).
if(nReadFile = write(1, buffer, nReadFile) == '\n')
If you want to check whether the currect character is a newline, you should to something like if (buffer[0] == '\n').
cout << nLineCount << endl;
This is C++, not C.