Why does the C scanf function not work in my MEX-file in MATLAB?

I have a C MEX-file, and I would like to have that file prompt the user for input when the file is run. To do this, I am using the C scanf function, which reads information from standard input. Here is the relevant code I am using:

printf("Enter number of minutes (0 - 59) =  ");

scanf("%d", #_minutes);

However, when this file is executed, the scanf function appears to be ignored, and the rest of the code is executed without waiting for user input.

Answer 1

[MathWorks Support Team]

This bug has been fixed in MATLAB 7.5 (R2007b). For previous product releases, read below for any possible workarounds:

Documentation on using C functions in MEX-files to prompt users for data is missing from the MATLAB external interfaces documentation. Here is additional information on using those functions:

The ability to access stdin or stdout is not available in MATLAB. Avoid trying to use printf and scanf in C MEX-files. To work around this issue:

1. Perform the input in MATLAB code, and design the MEX-file so that you pass the input value to the MEX-file.

2. Use mexCallMATLAB with the MATLAB function INPUT. Here is an example of how to do this:

mxArray *num_minutes, *str;

double out;

/* Replace the following two lines with the two code lines after them:

   * printf("Enter number of minutes (0 - 59) =  ");

   * scanf("%d", #_minutes);

   */

str = mxCreateString("Enter number of Minutes (0 - 59) =  ");

mexCallMATLAB(1,#_minutes,1,&str,"input");

/* The following is a test, to make sure we processed the input. */

out = mxGetScalar(num_minutes);

mexPrintf("This is really a double: %.0f ", out);

/* Need to free memory. */

mxFree(num_minutes);

mxFree(str);