Thread: Isdigit Problem

  1. #1
    Registered User
    Join Date
    Oct 2009

    Isdigit Problem

    I want to take the string tokens and test if they are integers. If not, an exception should be thrown. According to isdigit - C++ Reference , isdigit should return 0 if it is not a digit. But it is returning 0 for anything I input. Why is this? The code snippet is below.

    BinaryTree BinaryTree::setTree(char* str) {
        char* pStr = strtok(str, "()");
        BinaryTree result;
        while(pStr != NULL) {
            int token = atoi(pStr);
            if(isdigit(token) == 0) {
                std::cout<<pStr<<" is nTree"<<std::endl;
                std::cout<<token<<" is not an int."<<std::endl;
                throw InvalidInputException();

  2. #2
    Registered User NeonBlack's Avatar
    Join Date
    Nov 2007
    You're probably confused because isdigit()'s parameter is prototyped as int c. isdigit() returns true if c is in the range of '0' - '9', in other words, treat it like the parameter is a char.
    I copied it from the last program in which I passed a parameter, which would have been pre-1989 I guess. - esbo

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