Error Checking Integer C
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Check Input Is Integer In C
Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each c check for integer overflow other. Join them; it only takes a minute: Sign up Command line argument integer error checking in C up vote 0 down vote favorite I'm trying to successfully parse an integer from the arguments given on a command visual basic check integer line for C. The given input will look something like this: a.out 2 Very simple. However I cannot figure out how to have error checking on this. For example each of the following runs should throw an error: a.out 2hi a.out 9hello a.out 4x The error handling I have implemented catches any non-integer characters in front of the integer itself (e.g. "> a.out hi4") as I am using sscanf. Atoi() and strtol() don't work because they just
Python Check Integer
parse the integer value off the front of the argument. Any help would be greatly appreciated! c parsing error-handling integer share|improve this question asked Apr 14 '14 at 2:25 Nikkisixx2 469 Just loop over your argument and bellow if you encounter a non-digit then. What more could you ask for? BTW: scanf() allows whitespace before the number. –Deduplicator Apr 14 '14 at 2:28 add a comment| 2 Answers 2 active oldest votes up vote 0 down vote accepted Use strtol() and check that the end of what it converted is the end of the string: char *end; errno = 0; long l = strtol(argv[1], &end, 10); // 0 if you want octal/hex/decimal if (end == argv[i] || *end != '\0' || ((l == LONG_MIN || l == LONG_MAX) && errno == ERANGE)) …report problems… …either use l as a long, or check that it is in the range INT_MIN..INT_MAX This will skip quietly over leading blanks. If that's a problem, you can check for them too: if (!isdigit((unsigned char)argv[i]) && argv[i] != '+' && argv[i] != '-') …first character isn't part of a decimal number… See also: What is wrong with the following C code? Correct usage of strtol(). share|improve this answer edited Apr 14 '14 at 3:12 answered Apr 14 '14 at 3:07 Jonathan Leffler 438k61509822 add a comment| up vote 0 down vote int is_integer(char *st
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Integer Validation In C
4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Check if input is integer type in C up vote 8 down vote favorite 9 The catch is http://stackoverflow.com/questions/23051006/command-line-argument-integer-error-checking-in-c that I cannot use atoi or any other function like that (I'm pretty sure we're supposed to rely on mathematical operations). int num; scanf("%d",&num); if(/* num is not integer */) { printf("enter integer"); return; } I've tried: (num*2)/2 == num num%1==0 if(scanf("%d",&num)!=1) but none of these worked. Any ideas? c input integer share|improve this question edited Nov 1 '10 at 19:33 The Archetypal Paul 27.6k1578110 asked Nov 1 '10 at 19:04 Gal 7,1822168104 http://stackoverflow.com/questions/4072190/check-if-input-is-integer-type-in-c What do you mean "none of these worked"? And how did you try the last one? –David Thornley Nov 1 '10 at 19:52 @David I placed them in if statement, what is confusing about it? –Gal Nov 1 '10 at 19:54 What kind of input is "integer type"? One consisting only of digits? Is a minus sign allowed in the front? –eq- Nov 1 '10 at 20:05 You list two conditions and an if statement. I assume you didn't include an if statement in an if statement, so I don't know what you did there. (Did you just replace the if statement, or was it more significant than that?) Nor do you provide any clue to failure mode other than "none of these worked". Didn't compile? Run-time error? Didn't work the way you expected (and, if so, what did you expect?)? –David Thornley Nov 1 '10 at 21:10 @Gal are you asking if lets say some one gave 5.5 as an input and got a 5 ? because i'm not sure if that can be checked , and if so i would like to know how .. –eran otzap Apr 11 '12 at 14:51 add a comment| 11 Answers 11 active oldest votes up vo
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn http://stackoverflow.com/questions/9753346/determine-if-a-c-string-is-a-valid-int-in-c more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community http://www.microhowto.info/howto/safely_parse_an_integer_using_the_standard_c_library.html Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Determine if a C string is a valid int in error checking C up vote 16 down vote favorite 3 I need to check if a C string is a valid integer. I tried both int num=atoi(str); and int res=sscanf(str, "%d", &num); But sending the string "8 -9 10" in both of the lines returned simply 8, without indicating the invalidity of this string. Can anyone suggest an alternative? c string validation int share|improve this question edited Oct 16 '15 string to int at 20:29 royhowie 6,710112753 asked Mar 17 '12 at 20:14 sara 1,81942355 atoi does no error checking; its behavior if str doesn't contain a representation of an int value is undefined. (Typical implementations return 0.) sscanf is better, but its behavior is undefined if the value in the string is not representable as an int. Also, your title says you want to check for a valid int, but the body of your question says "valid integer"; they aren't the same thing. int is one of several integer types. –Keith Thompson Mar 18 '12 at 0:22 add a comment| 4 Answers 4 active oldest votes up vote 27 down vote accepted Have a look at strtol(), it can tell you about invalid parts of the string by pointer return. And beware of enthusiastic example code.. see the man page for comprehensive error-handling. share|improve this answer edited Mar 17 '12 at 20:34 answered Mar 17 '12 at 20:16 blueshift 4,3552546 strtol() just sets the pointer to the next "object" in the string. It does not validate anything. –user677656 Mar 17 '12 at 20:41 1 @g24l If that pointer ends up pointing to NULL, then you know the entire
click to enable Safely parse an integer using the standard C library Content 1 Objective 2 Background 3 Scenario 4 Methods 4.1 Method (signed integers) 4.2 Method (unsigned integers) 5 Variations5.1 Allowing partial conversion Tested on Debian (Etch, Lenny, Squeeze) Fedora (14) Ubuntu (Hardy, Intrepid, Jaunty, Karmic, Lucid, Maverick, Natty, Precise, Trusty) Objective To convert a string to an integer using the standard C library, giving an error for any input that is not a valid integer Background The standard library provides two sets of functions for parsing integers: the atoi family, which does not report errors, and the strtol family, which can report errors when used with care. Scenario Suppose that s is a pointer to the string to be parsed, which is null-terminated. Methods Method (signed integers) The following code fragment reports as an error any input string that cannot be converted in full: errno = 0; char* end = s; long int result = strtol(s,&end,10); if (errno == ERANGE) { printf("Error: integer overflow\n"); } else if (*end) { printf("Error: not a valid integer\n"); } else { printf("Result is: %ld",result); } You can replace strtol with strtoll provided you make a corresponding change to the result type. The third argument is the radix, which is decimal in this example but can be changed to any required value in the range 2 to 36. A radix of zero defaults to decimal, but allows octal with a prefix of ‘0’ and hexadecimal with a prefix of ‘0x’. Setting errno to zero is necessary because (unlike most standard library functions) strtol provides no other means to determine whether errno has been set. A return value of LONG_MIN or LONG_MAX is not a reliable indication because it could occur as the result of a valid input. Method (unsigned integers) The method for parsing unsigned integers is similar, however there is a com