C语言学习记录

获取数组长度，先计算数组的总字节大小，再除以单个元素字节数。与 python 不同的是，C 语言中数组存储的元素的类型和大小都是一样的。C 语言中，字符串实际都是字符数组，且字符串最后一个元素为 \0。

char sentences[][13] = {
	"Hello world1",
	"Hello world2",
	"Hello world3",
	"Hello world4",
	"Hello world5",
	"Hello world6"
};

int sentence_num = sizeof(sentences) / sizeof(sentences[0]);

通过 fgets 获取输入字符串，假如输入Hello world1，实际 search_for 指向的字符数组为 Hello world1\n\0 ，包括额外的\0和换行符这两个字符。而 strlen 计算字符串长度时，是排除结尾的\0后的长度，即Hello world\n的长度 。所以search_for[strlen(search_for) - 1]实际是Hello world1\n\0倒数第二个元素，替换后字符串为Hello world1\0\0。

	char search_for[14];
	printf("Search for: ");
	fgets(search_for, 14, stdin);
	printf("%i\n", strlen(search_for));
	search_for[strlen(search_for) - 1] = '\0';
	printf("%s\n", search_for);
	find_sentence(search_for);

strstr 要求查找的子串以\0结尾，以便获取子串的长度，但测试不以\0结尾也能正常查找。

char search_for2[] = {'H', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', '1'};
strstr(sentences[0], search_for2);

代码：

#include <stdio.h>
#include <string.h>

char sentences[][13] = {
	"Hello world1",
	"Hello world2",
	"Hello world3",
	"Hello world4",
	"Hello world5",
	"Hello world6"
};

int sentence_num = sizeof(sentences) / sizeof(sentences[0]);


void find_sentence(char search_for[]){
	int i;
	for(i = 0; i < sentence_num; i++){
		if(strstr(sentences[i], search_for)){
			printf("sentence %i: %s\n", i, sentences[i]);
		}
	}
}

int main(){
	char search_for[14];
	printf("Search for: ");
	fgets(search_for, 14, stdin);
	printf("%i\n", strlen(search_for));
	search_for[strlen(search_for) - 1] = '\0';
	printf("%s\n", search_for);
	find_sentence(search_for);
	
	//char search_for2[] = {'H', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', '1'};
	//find_sentence(search_for2);
	
	return 0;
}