深入理解C语言函数

深入理解strcpy函数

函数参数解析

strcpy(目的字符数组地址, 源字符数组地址);

应用方式1

int main(void) {
    char s1[81] = "China";
    char s2[81] = "India";
    strcpy(s1, s2);	//s2 -> s1
    puts(s1);
    return 0;
    //Output:India
}

应用方式2

int main(void) {
    char s1[81] = "China";
    char s2[81] = "India";
    strcpy(s1 + 2, s2 + 1);
    puts(s1);
    return 0;
    //Output:chndia
}

函数实现

void strcpy(char s1[], char s2[]) {
    int i = 0, j = 0;
    while (s2[i]) {
        s1[j++] = s2[i++];
    }
    s1[j++] = s2[i++];
    return;
}

优化

void strcpy(char s1[], char s2[]) {
    int i = 0, j = 0;
+   while (s1[j++] = s2[i++]) {}
-   while (s2[i]) {
-   	s1[j++] = s2[i++];
-   }
-   s1[j++] = s2[i++];
    return;
}

注意：

• 兼顾函数的高可用性和易读性
• 赋值表达式做条件时，先赋值，后做条件

✦将一个顺序表作为两个顺序表使用

删除一个字符串中的某个字符

样例：

“mydoghasabook” -> “mydghasabk”

程序样例1：

int main(void) {
    char s[] = "mydoghasabook";
    char key = 'o';
    int i = 0;
    while (s[i]) {
        if (s[i] - key) {
            i++;
        } else {
            //删除语句
            for (int j = i; s[j]; j++) {
                s[j] = s[j + 1];
            }
        }
    }
    puts(s);
    return 0;
}

优化

int main(void) {
    char s[] = "mydoghasabook";
    char key = 'o';
    int i = 0;
    while (s[i]) {
        if (s[i] - key) {
            i++;
        } else {
            //删除语句
            s[i] = 0;
            strcpy(s + i, s + i + 1);
            //strcat(s, s + i + 1);
        }
    }
    puts(s);
    return 0;
}

程序样例2

int main(void) {
    char s[] = "mydoghasabook";
    char key = 'o';
    int i = 0, j = 0;
    while (s[i]) {
        if (s[i] - key) {
            s[j++] = s[i];
        }
            i++;
    }
    s[j] = 0;
    puts(s);
    return 0;
}

优化

int main(void) {
    char s[] = "mydoghasabook";
    char key = 'o';
    int i = 0, j = 0;
    while (s[j++] = s[i]) {
        if (!(s[i++] - key)) {
            j--;
        }
    }
    puts(s);
    return 0;
}

优化2

int main(void) {
    char s[] = "mydoghasabook";
    char key = 'o';
    int i = 0, j = 0;
    for (; !(s[i] - key) || (s[j++] = s[i]); i++) {}
    puts(s);
    return 0;
}