C语言 如何在c中剪切字符串的一部分？
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原文地址: http://stackoverflow.com/questions/20342559/
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How to cut part of a string in c?
提问by answerSeeker
I'm trying to figure out how to cut part of a string in C. For example you have this character string "The dog died because a car hit him while it was crossing the road" how would a function go making the sentence "a car hit him while crossing the road" or "a car hit him"
我想弄清楚如何在 C 中剪切字符串的一部分。例如，你有这个字符串“狗死了，因为汽车在过马路时撞到了他”一个函数如何去使句子“a过马路时汽车撞了他”或“汽车撞了他”
How do you go about this with C's library (or/and) a custom function?
你如何使用 C 的库（或/和）自定义函数来解决这个问题？
ok I don't have the main code but this is going to be the structure of this experiment
好的，我没有主要代码，但这将是这个实验的结构
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <getopt.h>
#include "display_usage.c"/*If the user enters wrong arguments it will tell them how it should be */
void cut( const char *file, int option, int first, int last );
int main(int argc, char *argv[] ) {
FILE *fp;
char ch;
fp = fopen("test.txt", "r"); // Open file in Read mode
while (ch!=EOF) {
ch = fgetc(fp); // Read a Character
printf("%c", ch);
}
fclose(fp); // Close File after Reading
return 0;
}
void cut( const char *file, int reverse, int first, int last ) {
return;
}
采纳答案by M Oehm
The following function cuts a given range out of a char buffer. The range is identified by startng index and length. A negative length may be specified to indicate the range from the starting index to the end of the string.
以下函数从字符缓冲区中剪切给定范围。范围由起始索引和长度标识。可以指定负长度以指示从起始索引到字符串结尾的范围。
/*
* Remove given section from string. Negative len means remove
* everything up to the end.
*/
int str_cut(char *str, int begin, int len)
{
int l = strlen(str);
if (len < 0) len = l - begin;
if (begin + len > l) len = l - begin;
memmove(str + begin, str + begin + len, l - len + 1);
return len;
}
The char range is cut out by moving everything after the range including the terminating '\0'to the starting index with memmove, thereby overwriting the range. The text in the range is lost.
通过将范围之后的所有内容（包括终止符）移动'\0'到起始索引处memmove，字符范围被切掉，从而覆盖范围。范围内的文本丢失。
Note that you need to pass a char buffer whose contents can be changed. Don't pass string literals that are stored in read-only memory.
请注意，您需要传递一个其内容可以更改的字符缓冲区。不要传递存储在只读内存中的字符串文字。
回答by woolstar
strncpywill only copy up to ncharacters. Optionally you can move a pointer around in the string, and also stick a \0into the array to terminate it early if you have writable memory.
strncpy最多只能复制n字符。或者，您可以在字符串中移动一个指针，\0如果您有可写内存，也可以将 a 粘贴到数组中以尽早终止它。
回答by PADYMKO
For such problem, it is better to write own function, it will take time, but it will pay off. A code of a function str_sliceis shown below, is very similar to the JavaScripts's function string.slice(https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice) and to the Python's feature for making a slice on strings or arrays (https://docs.python.org/3.5/library/functions.html#slice).
对于这样的问题，最好自己编写函数，这需要时间，但会有所回报。函数str_slice 的代码如下所示，非常类似于 JavaScript 的函数string.slice( https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice) 和到 Python 的在字符串或数组上制作切片的功能（https://docs.python.org/3.5/library/functions.html#slice）。
It also based only on the C standard library, so must be cross-platform and to working with any compiler. If in doubt, to look on tests.
它也仅基于 C 标准库，因此必须是跨平台的并且可以与任何编译器一起使用。如有疑问，请查看测试。
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
/**
* Extracts a selection of string and return a new string or NULL.
* It supports both negative and positive indexes.
*/
char *
str_slice(char str[], int slice_from, int slice_to)
{
// if a string is empty, returns nothing
if (str[0] == '#include <assert.h>
void
test_str_slice()
{
char str[] = "abcdefghijkl";
assert(NULL == str_slice(str, -3, -10));
assert(NULL == str_slice(str, -1, -2));
assert(NULL == str_slice(str, -1, 0));
assert(NULL == str_slice(str, 1, 0));
assert(NULL == str_slice(str, 5, 4));
assert(NULL == str_slice(str, 0, 0));
assert(NULL == str_slice(str, 10, 10));
assert(NULL == str_slice(str, -2, -2));
assert(NULL == str_slice(str, -20, -12));
assert(NULL == str_slice(str, -20, -13));
assert(NULL == str_slice(str, 12, 13));
assert(NULL == str_slice(str, 12, 20));
assert(NULL == str_slice("", 1, 2));
assert(NULL == str_slice("", -2, -1));
assert(strcmp(str_slice(str, -3, -1), "jk") == 0);
assert(strcmp(str_slice(str, -8, -3), "efghi") == 0);
assert(strcmp(str_slice(str, -10, -9), "c") == 0);
assert(strcmp(str_slice(str, -2, -1), "k") == 0);
assert(strcmp(str_slice(str, -15, -1), "abcdefghijk") == 0);
assert(strcmp(str_slice(str, -12, -2), "abcdefghij") == 0);
assert(strcmp(str_slice(str, -15, -8), "abcd") == 0);
assert(strcmp(str_slice(str, -15, -11), "a") == 0);
assert(strcmp(str_slice(str, 1, 3), "bc") == 0);
assert(strcmp(str_slice(str, 11, 100), "l") == 0);
assert(strcmp(str_slice(str, 2, 4), "cd") == 0);
assert(strcmp(str_slice(str, 3, 6), "def") == 0);
assert(strcmp(str_slice(str, 0, 1), "a") == 0);
assert(strcmp(str_slice(str, 4, 6), "ef") == 0);
assert(strcmp(str_slice(str, 1, 2), "b") == 0);
assert(strcmp(str_slice(str, 0, 3), "abc") == 0);
assert(strcmp(str_slice(str, 0, 11), "abcdefghijk") == 0);
assert(strcmp(str_slice(str, 2, 10), "cdefghij") == 0);
assert(strcmp(str_slice(str, 0, 50), "abcdefghijkl") == 0);
}
')
return NULL;
char *buffer;
size_t str_len, buffer_len;
// for negative indexes "slice_from" must be less "slice_to"
if (slice_to < 0 && slice_from < slice_to) {
str_len = strlen(str);
// if "slice_to" goes beyond permissible limits
if (abs(slice_to) > str_len - 1)
return NULL;
// if "slice_from" goes beyond permissible limits
if (abs(slice_from) > str_len)
slice_from = (-1) * str_len;
buffer_len = slice_to - slice_from;
str += (str_len + slice_from);
// for positive indexes "slice_from" must be more "slice_to"
} else if (slice_from >= 0 && slice_to > slice_from) {
str_len = strlen(str);
// if "slice_from" goes beyond permissible limits
if (slice_from > str_len - 1)
return NULL;
buffer_len = slice_to - slice_from;
str += slice_from;
// otherwise, returns NULL
} else
return NULL;
buffer = calloc(buffer_len, sizeof(char));
strncpy(buffer, str, buffer_len);
return buffer;
}
Tests
测试
char *str = "A dog died because a car hit him while he was crossing the road.";
char *pCh = strstr(str, "dog");
As you can see in the tests, the function to returns a string or NULL. It also has support both negative and positive indexes. This idea taken from the mentioned early features from the JavaScript and Python. So, do not pollute this answer large amount of a text, I to recommend to you to read the docs of the JavaScript and the Python.
正如您在测试中看到的，该函数返回一个字符串或 NULL。它还支持负指数和正指数。这个想法取自前面提到的 JavaScript 和 Python 的早期特性。所以，不要大量污染这个答案，我建议你阅读 JavaScript 和 Python 的文档。
回答by Fiddling Bits
strstrwould be perfect for you, if you know the contents of the string.
strstr如果您知道字符串的内容，那对您来说将是完美的。
Example:
例子：
##代码##pChwill have the address of the 'd'in "dog".
pCh将有'd'in的地址"dog"。
回答by Digital_Reality
http://www.cplusplus.com/reference/cstring/
http://www.cplusplus.com/reference/cstring/
You can use functions like strstr (to get substring), strtok (split using some token),
您可以使用 strstr（获取子字符串）、strtok（使用某些标记拆分）等函数，
