Real simple question, regarding text file reading
Author
Sorry if you think this question is too easy to be on here, but this forum is the only one that I have a membership to.
I have a text file which is this format:
3 2 3 4
-3 1 1
1 -3 0
1 0 -4
-5 -5 0
Basically, first line has 4 numbers (each representing a specific variable values - the first nubmer which is 3, represents the dimension of the matrix), then second line through 4th line is a matrix (3 by 3 matrix), then the last line is the right-hand-side of that matrix. Thus I should be able to solve this linear equations eventually.
The problem comes from reading this file. At the moment I've got it so that:
infile >> dim >> ns >> s >> d; //Reads the first line (4 variables)
for (i = 1; i <= dim; i++) {
for (j = 1; j <= dim; j++) {
if (!(infile >> a[j])) {
cout << "Couldn't read a[" << i << "][" << j << "]" << endl;
exit(EXIT_FAILURE);
}
aa[j] = a[j];
}
}
This results in the exit always (end up with the "couldn't read a[1][1]" error message).
I think the problem is that it doesn't go to the next line after reading the first 4 variables, and i'm sure there's an easy way of fixing this problem but my head is blank at the moment.
Someone please help?
Could you post more code? A full, compilable example is often the best way to get help (feel free t cut out anything not related to the issue).
Author
Well I've put up all the essentials pretty much, I just have a few more lines above:
int *indx, s, d, ns;
int num, job=0, job2=0;
double p, **aa ;
double *x;
double sum;
ifstream infile;
string line2;
char * inname = "matrix.txt";
infile.open(inname);
if (!infile) {
cout << "Cannot open file " << inname << " for reading." << endl;
exit(EXIT_FAILURE);
}
... and the stuff I put up previously comes here
The reason for having string line2; is because I do something similar to this in another function with string line;.
So I had to use line2 to avoid redefinition.
int *indx, s, d, ns;
int num, job=0, job2=0;
double p, **aa ;
double *x;
double sum;
ifstream infile;
string line2;
char * inname = "matrix.txt";
infile.open(inname);
if (!infile) {
cout << "Cannot open file " << inname << " for reading." << endl;
exit(EXIT_FAILURE);
}
... and the stuff I put up previously comes here
The reason for having string line2; is because I do something similar to this in another function with string line;.
So I had to use line2 to avoid redefinition.
What is the type of "a"? Your have omitted the declarations of "a", "dim", "i" and "j". Please, paste a full source, and use [source][/source] tags to make a pretty box:
// like this!
If you were qualified to determine what was essential, you wouldn't have a problem. Post code. We've seen (and written) horrors you cannot imagine; you won't embarrass yourself. All you're doing is hindering our assistance.
Author
Sorry about not using boxes... I just don't know how to do it.
I have to test it if i'm doing it right.
I have to test it if i'm doing it right.
test
Author
Okay now I got that to work... here is the full code.
sorry for the inconvinience.
void matcalc3 (){ //Variables char read; int i, j, k; int ctner=0; ifstream inData; string line; char * name = "test.txt"; //Another file that is related to my work inData.open(name); if (!inData) { cerr << "Unable to open file"; exit(1); // call system to stop } if (inData.is_open()) { //Reads first line of the txt (#row, #col, #unknown) inData >> n; inData >> m; inData >> dim;... int *indx, s, d, ns; int num, job=0, job2=0; double p, **aa ; double *x; double sum; ifstream infile; string line2; char * inname = "matrix.txt"; infile.open(inname); if (!infile) { cout << "Cannot open file " << inname << " for reading." << endl; exit(EXIT_FAILURE); } //cout << "File " << inname; /*if (!(infile>>dim>>ns)){ cout << "\nFirst line must have size of system and number of rhs\n"; exit(EXIT_FAILURE); } if (ns < 1) { cout << "\nMust have at least one right-hand side vector\n"; exit(EXIT_FAILURE); }*/ /* make an "empty" loop to ignore the rest of the first line */ infile >> dim >> ns >> s >> d; //while (infile.get() != '\n'); indx = ivector(1, dim); /* holds pivot info from ludcmp for lubskp*/ //a = matrix(1, dim, 1, dim); /* this holds the original matrix */ aa = matrix(1, dim, 1, dim); /* a copy of the matrix to send to ludcmp */ //b = vector(1, dim); /* the original right-hand side */ x = vector(1, dim); /* Copy rhs to x and send to lubksp */ //cout << ": " << n << "x" << n << " matrix" << endl << endl; //cout << scientific << showpos; for (i=1; i<=dim; i++) { for (j=1; j<=dim; j++) { cout << "a[" << i <<"]["<<j<<"]="<<a[j]<<"\n"; } } for (i = 1; i <= dim; i++) { for (j = 1; j <= dim; j++) { if (!(infile >> a[j])) { cout << "Couldn't read a[" << i << "][" << j << "]" << endl; exit(EXIT_FAILURE); } aa[j] = a[j]; /* save a, work with aa */ //cout << setw(15) << a[j]; //shows input matrix } //cout << endl; } ludcmp(aa, dim, indx, &p); /* perform the decomposition */ for (num = 1; num <= ns; num++) { /* loop for the rhs vectors */ //cout << "\n=============================================\n"; /* Solve equations for each right-hand vector */ for (k = 1; k <= dim; k++) { /*if (!(infile >> b[k])) { cout <<"Couldn't read b[" << k << "]" << endl;; exit(EXIT_FAILURE); }*/ x[k] = b[k]; /* save b, work with x */ } lubksb(aa, dim, indx, x); /* back substitution for this rhs */ cout << "Solution:" << endl; for (j=0; j<=s-1; j++) { for (i=1; i<=d; i++) //for (i=j*d+1; i<=d*(j+1); i++) { if (type[j*d+i]==0) { cout << setw(10) << setprecision (3) << pres[j*d+i]; } else if (type[j*d+i]==3) { cout << setw(10) << " "; } else if (type[j*d+i]==2) { job+=1; cout << setw(10) << setprecision (3) << x[job]; pres[j*d+i] = x[job]; } else if (type[j*d+i]==1) { cout << setw(10) << setprecision (3) << pres[j*d+i]; //used to be just 'i' } } cout << '\n'; } cout << endl << endl; /*cout << "Right-hand side:" << endl; for (i = 1; i <= n; i++) { cout << setw(15) << b; } cout << endl; cout << "Matrix * solution:" << endl; for (i = 1; i <= n; i++) { sum = 0.0; for (j = 1; j <= n; j++) { sum += a[j] * x[j]; } cout << setw(15) << sum; }*/ } cout << "\n================================================================\n\n"; //Writing solution to txt ofstream solfile ("solution.txt"); if (solfile.is_open()) { solfile << "Solution:" <<"\n"; for (j = 0; j <= s-1; j++) { for (i=1; i<=d; i++) //for (i=j*d+1; i<=d*(j+1); i++) { if (type[j*d+i]==0) { solfile << setw(10) << setprecision (3) << pres[j*d+i]; } else if (type[j*d+i]==3) { solfile << setw(10) << " "; } else if (type[j*d+i]==2) { job2+=1; solfile << setw(10) << setprecision (3) << x[job2]; } else if (type[j*d+i]==1) { solfile << setw(10) << setprecision (3) << pres[j*d+i]; } } solfile << "\n"; } } infile.close(); free_vector(b, 1, dim); free_matrix(a, 1, dim, 1, dim); free_matrix(aa, 1, dim, 1, dim); free_vector(x, 1, dim); free_ivector(indx, 1, dim); cout << "Solution file written." << "\n"; //cout << "xcount = " << xcount << "\n"; } //eopsorry for the inconvinience.
Author
By the way,
"a" and "dim" are declared else where as:
double **a;
a = dmatrix(1, dim, 1, dim);
int dim;
same with some other variables if you happen to wonder where it's declaration is.
Program runs , it just that it exits due to the exit setup I have. (But ideal I wouldn't want that exit 'if' to satisfy.
"a" and "dim" are declared else where as:
double **a;
a = dmatrix(1, dim, 1, dim);
int dim;
same with some other variables if you happen to wonder where it's declaration is.
Program runs , it just that it exits due to the exit setup I have. (But ideal I wouldn't want that exit 'if' to satisfy.
What type is a? Is it a double pointer? How many doubles is it initialised to point at, given that you've commented out this line "a = matrix(1, dim, 1, dim);"?
If anyone is inconvenienced, it is you. By providing us with a compilable example, you give us everything we need to help you. I cannot compile your code, because I don't have the functions "matrix()" and "vector()". Therefore I cannot reproduce the problems you are having directly.
In any case, I think you should look carefully at your array indexing. Arrays in C++ are 0 based. In general, to loop N times, in C++ we write:
You should be able to see that this loops the same number of times as i = 1 ; i <= N...
If anyone is inconvenienced, it is you. By providing us with a compilable example, you give us everything we need to help you. I cannot compile your code, because I don't have the functions "matrix()" and "vector()". Therefore I cannot reproduce the problems you are having directly.
In any case, I think you should look carefully at your array indexing. Arrays in C++ are 0 based. In general, to loop N times, in C++ we write:
for( int i = 0 ; i < N ; ++i ){ // loop body}You should be able to see that this loops the same number of times as i = 1 ; i <= N...
Author
Sorry but it just is not possible for me to post the ENTIRE code, I've got 6 header files with each of them having at least 500 lines, and I also include GLUT and nrutil (numerical recipe) stuff. I suppose the vector(), matrix() bit comes from the numerical recipe headers.
The intention of my code is not to be able to read this file, this is only a small small part of what I'm trying to achieve.
I just need to know how to read the next line, after reading the first line.
Is it not possible to give me a tip regarding that without looking at my gazzilion lines of code?
The intention of my code is not to be able to read this file, this is only a small small part of what I'm trying to achieve.
I just need to know how to read the next line, after reading the first line.
Is it not possible to give me a tip regarding that without looking at my gazzilion lines of code?
This topic is closed to new replies.
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