🚀 go-pugleaf

Edward J. Hartnett (ejh@khonshu.colorado.edu) wrote:
: 
: Hi, Here's a section from my program:
: 
: main() {
:   int lat_zone;
:   int cell, isccp_cell, isccp_num;
:   float lat, lon;
:   float centlat[NUM_LAT_ZONES], centlon[MAX_ISCCP_NUM];
: 
:   equare();
: 
:   printf("Please enter the lat and long in degrees: ");
:   scanf("%f%f",&lat, &lon);
:   printf("%f, %f",lat,lon);
: 
: And here's what I get when I try to run this program:
: 
: > iscgrid
: Please enter the lat and long in degrees: 1.0, 1.0
: Segmentation fault
: >
: 
: 
: So obviously something is wrong with my scanf call, but what? I asked
: the guru here and he said he never uses scanf, he uses fgets to read
: from the input to a character array and then uses scanf to read that.
: Is this common proactice? Is there some better way? All advice
: welcome!
: 
: Thanks.
: --
I agree with your guru.
But if you really want to easily get into trouble you can still use scanf()
The following program compiles and runs without problems.

s1.146% cat test.c
main() {
  float lat, lon;

  printf("Please enter the lat and long in degrees: ");
  scanf("%f%f",&lat, &lon);
  printf("\n%f, %f\n",lat,lon);
}
s1.147% gcc !$
gcc test.c
s1.148% a.out
Please enter the lat and long in degrees: 1.0 2.0

1.000000, 2.000000
s1.149% echo "Now a problem will come"
Now a problem will come
s1.150% a.out
Please enter the lat and long in degrees: 1.0, 1.0

1.000000, 0.000000

Note however that there should be no "," in the input (cf 148 and 150).
I suspect that a comma might have created the problem in your program.

Scanf is fragile, especially for an incorrect input, therefore a common
(I think) practice is to read a line, tokenise it and process each
token separately.

Marek Makowski
-- 
                  Marek Makowski  | Email: marek@iiasa.ac.at
         International Institute  | Phone: +43 02236 71.5210
     for Applied System Analysis  | Fax:   +43 02236 71.313
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