sscanf not reading numbers

Question

A newbie in C is trying to extract two numbers from a string using sscanf(). The numbers shall be parsed from strings formatted like "7-12", which should result in firstNode = 7and secondNode = 12. So I want to get the numbers, the minus sign can be understood as a number seperator. My current implementation is similar to the example I found on this SO answer:

void extractEdge(char *string) { int firstNode = 123; int secondNode = 123; sscanf(string, "%*[^0123456789]%u%*[^0123456789]%u", &firstNode, &secondNode); printf("Edge parsing results: Arguments are %s, %d, %d", string, firstNode, secondNode); }

But if I execute the code above, there always is retourned the inital value 123 for both ints. Note that the output of string gives the correct input String, so I think an invalid string can't be a probable cause for this problem.

Any ideas why the code is not working? Thanks in advance for your help.

%*[^0123456789] has to match at least one character. If your string starts with 7, that means %*[] fails, and makes sscanf return. Why not just scanf("%d-%d"? — KamilCuk
– KamilCuk, Commented Nov 19, 2020 at 13:39
That works! Wouldn't have thought that posix could be that easy sometimes, regarding the examples on the internet. — BenjyTec
– BenjyTec, Commented Nov 19, 2020 at 13:51

MikeCAT · Accepted Answer · 2020-11-19 13:40:34Z

%*[^0123456789] requires one or more non-digit character, but the first character of you input 7-12 is a digit. This makes sscanf() stop there and read nothing.

Remove that and use "%d%*[^0123456789]%d" as format specifier to deal with 7-12.

Also note that correct format specifier for reading decimal int is %d, not %u. %u is for reading unsigned int.

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