Why does the C scanf function not work in my MEX-file in MATLAB?
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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.
Accepted Answer
MathWorks Support Team
on 22 Jan 2010
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);
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on 22 Jan 2010
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