Question

In GNU Octave, I’m getting an error with this code.

A = cell(10,1);
A{5,1} = "foobar";
outputFile = fopen("mytext.txt", "w");
printf(outputFile, "%s", A{5,1});

I get this error:

error: printf: format TEMPLATE must be a string

This error message is not Helpful, The google does not know what this error is! what is wrong?

Answer 1

Found the solution to this error.

The very first parameter you are passing into printf MUST be a valid format string. You are passing it a file handle. If you want to pass a file handle, you should be using fprintf instead. If you specify a first parameter as a file, printf gives you the above error.

You should be doing this instead:

A = cell(10,1);
A{5,1} = "foobar";
outputFile = fopen("mytext.txt", "w");
fprintf(outputFile, "%s", A{5,1});        

Or, if you wanted to print to the screen, remove the outputFile parameter:

A = cell(10,1);
A{5,1} = "foobar";
outputFile = fopen("mytext.txt", "w");
printf("%s", A{5,1});
% Here printf successfully casts the cell as a string.  no error.

You are passing bad parameters to printf and Octave tries to make sense of nonsense. Review this webpage to see what can and cannot be passed into octave’s printf:

http://www.gnu.org/software/octave/doc/interpreter/Formatted-Output.html#doc-printf