‘true’ undeclared (first use in this function) in opencv

c, opencv

Solution

Replace it with e.g.

while(1)

or

for(;;)

or you can do (defining `c` before the loop):

while (c != 27)
{
    //grab each frame sequentially
    IplImage* frame = cvQueryFrame( capture );
    if (!frame)
        break;
    //show the retrieved frame in the window
    cvShowImage("BLINK", frame);
    //wait for 20 ms
    c = cvWaitKey(20);
    //exit the loop if user press "Esc" key
}

or without `c` at all, but this will start the loop with a 20ms wait:

while (cvWaitKey(20) != 27)
{
    //grab each frame sequentially
    IplImage* frame = cvQueryFrame( capture );
    if (!frame)
        break;
    //show the retrieved frame in the window
    cvShowImage("BLINK", frame);
}

And a third possibility:

for(;;)
{
    //grab each frame sequentially
    IplImage* frame = cvQueryFrame( capture );
    if (!frame)
        break;
    //show the retrieved frame in the window
    cvShowImage("BLINK", frame);
    if (cvWaitKey(20) == 27)
        break;
}

UPDATE: while wondering whether it would be more correct to define

#define true  1
#define false 0

or

#define true 1
#define false (!true)

or again

#define false 0
#define true  (!false)

because if I, say, did:

int a = 5;
if (a == true) { // This is false. a is 5 and not 1. So a is not true }
if (a == false){ // This too is false. So a is not false              }

I would come up with a really weird result, I found this link to a slightly weirder result.

I suspect that to solve this in a safe way would require some macro such as

#define IS_FALSE(a)  (0 == (a))
#define IS_TRUE(a)   (!IS_FALSE(a))

Problem

Original source

Related problems

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