Bscis Knowledge(Function)
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extern unsigned int strlen(char *s)
计算字符串s的(unsigned int)长度,不包括(‘\0’)
int strlen(const char *str){ assert(str!=nullptr); int len=0; while((*str++) != '\0') len++; return len;}
void *memest(void *s, int ch, size_t count)
将s中前n个字节 (typedef unsigned int size_t)用 ch 替换并返回 s .作用是在一段内存块中填充某个给定的值,它是对较大的结构体或数组进行清零操作的一种最快方法
void *memest(void *src, int ch, size_t count){ assert(str!=nullptr); char *tmpsrc = (char*)src; while(count--) *tmpsrc++ = (char)ch; return src;}
void *memcpy(void *dst, const void *src, size_t n)
从源src所指的内存地址其实位置开始拷贝n个字节到目标dest所指的内存地址的起始位置中
void *memcpy(void *dst, const void *src, size_t num){ assert((dst!=nullptr) && (scr!=nullptr)); assert(des >= scr+num || scr > dst+num);//内存重叠 byte *psrc = (byte*)src;//byte即为unsigned char类型 byte *pdst = (byte*)dst; while(num-- > 0) *pdst++ = *psrc++;//先取值,再指向下一位 return dst;}
void memmove(void dest, const void* src, size_t count)
memmove用于从src拷贝count个字符到dest,如果目标区域和源区域有重叠的话,memmove能够保证源串在被覆盖之前将重叠区域的字节拷贝到目标区域中。但复制后src内容会被更改。但是当目标区域与源区域没有重叠则和memcpy函数功能相同
void* memmove(void* dest, void* source, size_t count) { void* ret = dest; if (dest <= source || dest >= (source + count)) { //Non-Overlapping Buffers //copy from lower addresses to higher addresses while (count --) *dest++ = *source++; } else { //Overlapping Buffers //copy from higher addresses to lower addresses dest += count - 1;source += count - 1; while (count--) *dest-- = *source--; } return ret; }
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