在C中返回值

Question

我在編寫的二進制搜索中返回值存在問題。

我有以下：

INT的binarySearch（字符*指令[]，INT低，INT高，字符*串）;

int main() { 
    char *instructions[]; // some array of strings - it does not include the string "jk" 
    char *string = "jk"; 
    int high = inst_len; 
    int x = binarySearch(instructions, 0, high, string); 
    if (x == -1) 
     printf("not found"); 
    else if (x == -2) 
    printf("error"); 
    else 
    printf("Found at %d", x); 
} 

int binarySearch(char *instructions[], int low, int high, char *string) { 

    int mid = low + (high - low)/2; 

    // Not found 
    if (high <= low) 
     return -1; 

    // If instructions[mid] is less than string 
    else if (strcmp(instructions[mid], string) > 0) 
     binarySearch(instructions, low, mid-1, string); 

    // If instructions[mid] is larger than string 
    else if (strcmp(instructions[mid], string) < 0) 
     binarySearch(instructions, mid+1, high, string); 

    // Return position 
    else 
     return mid; 
} 

無論怎樣，在main，的binarySearch總是返回0。但是，當我把打印語句的二進制搜索算法，我得到的返回-1。這是爲什麼發生？這很奇怪！

Answer 1

你想這樣的：

// If instructions[mid] is less than string 
else if (strcmp(instructions[mid], string) > 0) 
    return binarySearch(instructions, low, mid-1, string); 

// If instructions[mid] is larger than string 
else if (strcmp(instructions[mid], string) < 0) 
    return binarySearch(instructions, mid+1, high, string); 

注意 「return」 的一部分。

你也在做比較比你更多的時間;你可以存儲的strcmp的結果，所以你只這樣做一次：

int r = strcmp(instructions[mid], string); 

if (r > 0) 
    return binarySearch(instructions, low, mid-1, string); 
else if (r < 0) 
    return binarySearch(instructions, mid+1, high, string);