Question

I have a question regarding passing a variable that is a char array from one function into the next.

Here are the samples of code involved:

int main( int argc, char** argv )
{

int value = 0;

int nCounter = 0;
FILE* fIn = NULL;
char * sLine = new char[MAX_FILENAME_SIZE];
char * sFileName = new char [MAX_FILENAME_SIZE];
char * s = new char [MAX_FILENAME_SIZE];



if ((fIn = fopen(ImgListFileName,"rt"))==NULL)

{
    printf("Failed to open file: %s\n",ImgListFileName);
    return nCounter;
}



while(!feof(fIn)){

//set the variables to 0
memset(sLine,0,MAX_FILENAME_SIZE*sizeof(char));
memset(sFileName,0,MAX_FILENAME_SIZE*sizeof(char));
memset(s,0,MAX_FILENAME_SIZE*sizeof(char));
//read one line (one image filename)
//sLine will contain one line from the text file
fgets(sLine,MAX_FILENAME_SIZE,fIn);
//copy the filename into variable s
strncpy(s, sLine, strlen(sLine)-1);
//put a \0 character at the end of the filename
strcat(sLine,"\0");
//create the filename
strcat(sFileName,s);

nCounter++;


fclose(fIn);
delete sLine;
delete sFileName;
delete s;
    const int size = 60;
    char path[size] = "path";
    strcat(path,sFileName);

    printf (path);
IplImage *img = cvLoadImage(path);
detect_and_draw(img);
cvWaitKey();
cvReleaseImage(&img);
cvDestroyWindow("result");

void detect_and_draw( IplImage* img )
{


More code that isn't involved....


cvSaveImage(sFileName, img);

Now, I have tried the following:

void getFilename(char * sFileName)
{
    printf("The filename is %s\n", sFileName);
    return;
}

And then call with

char * S ="string"
getFilename(S);
cvSaveImage(S,img);

But “string” is placed into “The filename is: string”.

What can I do so that I can use sFileName, the char array, in cvSaveImage(sFileName, img)?

Thanks in advance, and if you need any further clarifications, please ask!

Answer 1

If I’m understanding correctly, what you have is a scoping problem. You essentially have:

int main(/* */)
{ char sFileName[MAX_FILENAME_SIZE];

  /* code to initialize sFileName to contain a value */

  detect_and_draw(img);
}

void detect_and_draw(IplImage *img)
{ cvSaveImage(sFileName, img);
}

The problem is that sFileName is local to main() and not accessible in detect_and_draw(). You can either modify detect_and_draw() to take a second argument:

int main()
{ /* stuff */
  detect_and_draw(img, sFileName);
}
void detect_and_draw(IplImage *img, const char* fn)
{ cvSaveImage(fn, img);
}

Or make sFileName a global variable declared/defined outside the scope of main() – although that’s quite often considered to be an inferior solution.