sscanf（）双显示零

Question

I'm having troubles with sscanf() function to read doubles. I have a comma separated text file like this:

ABC,DEF,0.465798,0.754314
GHI,JKL,0.784613,0.135264
MNO,OPQ,0.489614,0.745812
etc.

So first I get the line with fgets() and then I use sscanf() to get the two string and two double variables.

fgets(buffer, 28, file);
sscanf(buffer, "%4[^,],%4[^,],%lf[^,],%lf[^\n]", string1, string2, &double1, &double2);

printf("%s %s %f %f\n", string1, string2, double1, double2);

But the output is:

ABC DEF 0.465798 0.000000
GHI JKL 0.784613 0.000000
MNO OPQ 0.489614 0.000000

So somehow it doesn't scan the last float. I've tried %lf[^ \\t\\n\\r\\v\\f,] and just %lf but it still doesn't work.

Answer 1

Unless your variables double1 and double2 are pointers, you will get undefined behavior.

You need to use the address-of operator & to get a pointer to those variables:

sscanf(buffer, "%3s,%3s,%lf,%lf", string1, string2, &double1, &double2);

Answer 2

Change

"%4[^,],%4[^,],%lf[^,],%lf[^\n]"

To

int result;
result = sscanf(buffer, "%4[^,],%4[^,],%lf,%lf", string1, string2, &double1, &double2);
if (result != 4) // handle error

Notice the & on double1 and double2 - likley a typo.

Also strongly recommend to check that the result is 4. Not checking the sscanf() result is really core to this question. The "zeros" printed out are the result of double2 not having been scanned and retained its previous value which could have been anything. Had the sscanf() result been checked it would have reported 3, showing the problem was between scanning double1 and double2 . But in the larger scene, it is good practice to verify all the expected values were scanned before going on.

Answer 3

sscanf(buffer, "%4[^,],%4[^,],%lf[^,],%lf[^\n]", string1, string2, double1, double2);

should be

sscanf(buffer, "%3s,%3s,%lf,%lf", string1, string2, &double1, &double2);

Note & (address of) for doubles

Answer 4

The reason that your code didn't work is because:

sscanf(buffer, "%4[^,],%4[^,],%lf[^,],%lf[^\n]", string1, string2, &double1, &double2);

%[...] and %[^...] are actually conversion types, like %d , %x , and they match/don't match sequence of listed characters, ending with ] . Notice that you don't have to provide %s , even though you're parsing string.

Your problem was that you combined two type of conversion types, %lf and [^...] , scanf actually sees the later part as the string to match, so for instance following code would successfully parse the string:

char *b = "ABC,DEF,0.465798[^,],0.754314[^\n]\n";
sscanf(b, "%4[^,],%4[^,],%lf[^,],%lf[^\n]", string1, string2, &double1, &double2);

The easiest solution is to leave [^,] part (chux's solution):

sscanf(b, "%4[^,],%4[^,],%lf,%lf", string1, string2, &double1, &double2);

Or use field width (Joachim Pileborg, and David RF's solution):

sscanf(buffer, "%3s,%3s,%lf,%lf", string1, string2, &double1, &double2);