重写C语言strcpy()、strncpy()函数

1. strcpy()、strncpy()函数

原型:

**char *strcpy(char dest, const char src);
**char *strncpy(char dest, const char src, size_t n);

1. strcpy函数为将src字符串全部赋值到dest字符串，如果本来strlen(dest) > strlen(src)，那么调用strcpy后，dest的字符串长度和src的字符串长度相等
2. strncpy函数为将src的n个字符复制到dest字符串中,赋值后dest的strlen为n，如果n >= strlen(src)那么此时调用strncpy相当于调用strcpy()函数，即全部复制过去

2. 示例代码

1.重写strcpy()

/********************************************************************
 *strcpy(char *dest, const char *src)函数：
 *dest和src需要有空间，即dest和src需要是字符串数组或者动态分配了空间
 ********************************************************************/
void Strcpy(char *dest, const char *src) {	
	int length = 0;
	int i = 0;
	length = strlen(src);
	
	while('\0' != src[i]) {		
		dest[i] = src[i];
		i ++;
	}
	dest[i] = '\0';
}

2.重写strncpy()

void Strncpy(char *dest, const char *src, size_t n) {
	int length = strlen(src);
	if(n >= length) {
		Strcpy(dest, src);
		return ;
	}
	
	int i = 0;
	while(('\0' != src[i]) && (i < n)) {
		dest[i] = src[i];
		i ++;
	}
	dest[n] = '\0';
}

3.测试代码

注意strcpy、strncpy函数的参数必须有空间，如若没有则必须手动分配，否则会出现段错误

int main(int argc, char *argv[]) {
//[情况一:(对于字符串数组)]
	char dest1[32];
	char src1[32];
	int n;
	printf("请输入原字符串: ");
	scanf("%s", src1);
	printf("请输入目标字符串:");
	scanf("%s", dest1);

	//strcpy
	Strcpy(dest1, src1);
	printf("after strcpy 情况一: \n");
	printf("dest1 string = %s, src1 string = %s\n", dest1, src1);
	//strncpy
	printf("请输入要赋值的位数:");
	scanf("%d", &n);
	Strncpy(dest1, src1, n);
	printf("after strncpy 情况一: \n");
	printf("dest1 string = %s, src1 string = %s\n", dest1, src1);
//[情况二:(char *指针)]
	char *dest;
	char *src;
	char *temp;

	printf("请输入原字符串: ");
	scanf("%s", temp);
	dest = (char *)malloc(strlen(temp) + 1);
	src = (char *)malloc(strlen(temp) + 1);
	src = temp;
	printf("请输入目标字符串:");
	scanf("%s", dest);

	//strcpy
	Strcpy(dest, src);
	printf("after strcpy 情况一: \n");
	printf("dest string = %s, src string = %s\n", dest, src);

	//strncpy
	printf("请输入要赋值的位数:");
	scanf("%d", &n);
	Strncpy(dest, src, n);
	printf("after strncpy 情况二: \n");
	printf("dest1 string = %s, src1 string = %s\n", dest, src);

	return 0;
}

3.运行结果图

已在ubuntu16.04 vim编辑器编辑，gcc编译通过