在这笔记里面，记录着一些c语言平常的疑问，用来让自己可以快速记住一些特殊的地方
Why use strcmp instead of == in C
strcmp compares the actual C-string content, while using == between two C-string is asking if this two char pointers point to the same position.
下面举例几个C-sting的例子
char string_a[] = "foo";
char string_b[] = "foo";
char * string_c = string_a;
strcmp(string_a, string_b) == 0 would return true, while string_a == string_b would return false. Only when "comparing" string_a and string_c using == would return true.
If you want to compare the actual contents of two C-string but not whether they are just alias of each other, use strcmp.
用qsort对字符串数组排序
qsort用来对字符串数组排序需要注意的地方，我们先看一下qsort的函数
void qsort(void *base, size_t nmemb, size_t size,int (*compar)(const void *, const void *));
分别说一下这个参数的意思
- base: 字符串数组的的首地址
- nmem: 数组元素的个数，这里其实就是字符串的个数
- size: 每个元素的大小，这里每个元素都是指针变量，因此大小并不是字符串的小心，而是指针变量的大小，即sizeof(char *)
- int (*compar)(const void*,const void*): 这里需要传入一个比较函数，下面说一下这个函数要注意的地方
找个例子来试试
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
int myCompare (const void * a, const void * b ) {
const char *pa = *(const char**)a;
const char *pb = *(const char**)b;
return strcmp(pa,pb);
}
int main() {
int i;
const char *input[] = {"a","orange","apple","mobile","car"};
int stringLen = sizeof(input) / sizeof(char *);
qsort(input, stringLen, sizeof(char *), myCompare);
for (i=0; i<stringLen; ++i)
printf("%d: %s\n", i, input[i]);
}
