在Objective-C中使用塊

Question

const char *sentence = "He was not in the cab at the time.";

printf("\"%s\" has %d spaces\n", sentence, (int) ^ {
    int i = 0;
     int countSpaces = 0;

    while (sentence[i] != '\0') {
        if (sentence[i] == 0x20) {
            countSpaces++;
        }
        i++;
    }    
    return countSpaces;
});

這段代碼只計算一個字符串中的空格，但由於某種原因，它表示1606416608個空格而不是8個。我不確定出了什么問題，所以感謝您的幫助！

Answer 1

您將實際塊傳遞給printf ，而不是塊的結果。 相反，試試吧

const char *sentence = "He was not in the cab at the time.";

printf("\"%s\" has %d spaces\n", sentence, (int) ^ {
    int i = 0;
    int countSpaces = 0;

    while (sentence[i] != '\0') {
        if (sentence[i] == 0x20) {
            countSpaces++;
        }
        i++;
    }    
    return countSpaces;
}()); // <-- note the extra parentheses here, indicating that you're calling the block