对于一些背景，我对C不太熟悉，但我对Java非常精通。在我正在处理的当前程序中，我试图弄清楚如何实现与 java 方法 someString.substring(int startIndex, int endIndex) 完全相同的东西，它根据前一个字符串的开始和结束索引返回一个新字符串。
为了实现的目的，我只会删除第一个字符并返回剩余的字符串。这是我在 java 中的实现。
public String cut_string(String word)
{
String temp = word.substring(1, word.length());
return temp;
}
【问题讨论】：
使用类似的东西
#include <stdio.h>
#include <stdlib.h>
char* substring(char*, int, int);
int main()
{
char string[100], *pointer;
int position, length;
printf("Input a string\n");
gets(string);
printf("Enter the position and length of substring\n");
scanf("%d%d",&position, &length);
pointer = substring( string, position, length);
printf("Required substring is \"%s\"\n", pointer);
free(pointer);
return 0;
}
/*C substring function: It returns a pointer to the substring */
char *substring(char *string, int position, int length)
{
char *pointer;
int c;
pointer = malloc(length+1);
if (pointer == NULL)
{
printf("Unable to allocate memory.\n");
exit(1);
}
for (c = 0 ; c < length ; c++)
{
*(pointer+c) = *(string+position-1);
string++;
}
*(pointer+c) = '\0';
return pointer;
}
【讨论】：
应该这样做：
char* cut_string(char const* in)
{
// Compute the length of the input string and use
// that length to allocate memory for the string to
// be returned.
// strlen(in) returns the length of the string.
// malloc(...) allocates memory.
char* ret = malloc(strlen(in));
if ( ret == NULL )
{
// If there is a problem in allocating memory
// return NULL. We can't do anything about
// cutting the input string.
return NULL;
}
// Copy the input string to the string to be returned.
// Start copying from the second character. If
// in is "This is a string", in+1 is "his is a string".
strcpy(ret, in+1);
// Return the resulting string.
return ret;
}
在调用函数中，
char* s = cut_string("my string");
if ( s != NULL )
{
// Use s
// Make sure to free the memory returned by cut_string.
free(s);
}
【讨论】：