[英]char array variables are destroyed after exiting from function
I use strtok()
to tokenize my string in a function. After copying the values to a global char
array, I print the values to ensure the functionality.我使用strtok()
在 function 中标记我的字符串。将值复制到全局char
数组后,我打印这些值以确保功能。 Everything is OK, but when I want to access them they are destroyed.一切都很好,但是当我想访问它们时,它们被破坏了。
this is the code:这是代码:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
int client, count = 0;
volatile char *token_temp[30];
volatile int toknum = 0;
int text_test()
{
char my_tokenised_string_buffer[255] = "Response\n\nCompany\nModel\nRevision: N01234567890\n\nOK";
const char delimiters[3] = "\n";
char *token = strtok(my_tokenised_string_buffer, delimiters);
token_temp[0]= token;
printf("first tokenised value = %s\n", token);
while (token != NULL) {
++toknum;
token = strtok(NULL, delimiters);
token_temp[toknum]= token;
printf("toknum : %d\t", toknum);
printf("token id from inside tokenise loop : %s -> [%u]\n", token_temp[toknum], toknum);
}
printf("\n\n\n");
for (int i = 0; i < toknum; i++) {
printf("token [%d] value in function out of tokenise = %s\n", i, token_temp[i]);
}
return 0;
}
int main()
{
text_test();
printf("\n\n\n");
for (int i = 0; i < toknum; i++) {
printf("token [%d] value in main = %s\n", i, (char *)token_temp[i]);
}
return 0;
}
I want to assign the values to structures but they are missed.我想将值分配给结构,但它们被遗漏了。
Within the function there is declared a local array with automatic storage duration在 function 中声明了一个具有自动存储持续时间的本地数组
int text_test()
{
char my_tokenised_string_buffer[255] = "Response\n\nCompany\nModel\nRevision: N01234567890\n\nOK";
//...
that will not be alive after exiting the function.退出function后就不会活着了。
So the array of pointers所以指针数组
volatile char *token_temp[30];
will contain invalid pointers and dereferencing these pointers will invoke undefined behavior.将包含无效指针并且取消引用这些指针将调用未定义的行为。
What you need is for example to allocate dynamically a character array for each string extracted from the array my_tokenised_string_buffer
.例如,您需要为从数组my_tokenised_string_buffer
中提取的每个字符串动态分配一个字符数组。
Another approach is declare the array my_tokenised_string_buffer
as having static storage duration specifying the keyword static
另一种方法是将数组my_tokenised_string_buffer
声明为具有 static 存储持续时间,指定关键字static
static char my_tokenised_string_buffer[255] = "Response\n\nCompany\nModel\nRevision: N01234567890\n\nOK";
The thing is that the strtok
calls gives pointers to slices of your my_tokenised_string_buffer
.问题是strtok
调用给出了指向my_tokenised_string_buffer
切片的指针。 But by exiting the function, my_tokenised_string_buffer
gets out of scope, thus being overridden with new data you put in the stack.但是通过退出 function, my_tokenised_string_buffer
从 scope 中退出,因此被您放入堆栈的新数据覆盖。 To avoid this, you have 2 solutions:为避免这种情况,您有两种解决方案:
Or my_tokenised_string_buffer
never goes out of scope, making the following program:或者my_tokenised_string_buffer
永远不会出scope,做如下程序:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
int client, count =0;
volatile char *token_temp[30];
volatile int toknum = 0;
char my_tokenised_string_buffer[255] = "Response\n\nCompany\nModel\nRevision: N01234567890\n\nOK"; // Static, so won't go out of scope
int text_test()
{
const char delimiters[3] = "\n";
char *token = strtok(my_tokenised_string_buffer, delimiters);
token_temp[0]= token;
printf("first tokenised value = %s\n",token);
while (token != NULL)
{
++toknum ;
token = strtok(NULL, delimiters);
token_temp[toknum]= token;
printf("toknum : %d\t",toknum);
printf("token id from inside tokenise loop : %s -> [%u]\n", token_temp[toknum], toknum);
}
printf("\n\n\n");
for(int i = 0; i < toknum;i++)
{
printf("token [%d] value in function out of tokenise = %s\n",i, token_temp[i]);
}
return 0;
}
int main()
{
text_test();
printf("\n\n\n");
for(int i = 0; i < toknum;i++)
{
printf("token [%d] value in main = %s\n",i, token_temp[i]);
}
return 0;
}
or you copy your tokens each time you get a new one, with a malloc. However, you'll need to manage the last token differently:或者您每次获得新令牌时都使用 malloc 复制您的令牌。但是,您需要以不同方式管理最后一个令牌:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <stdlib.h>
int client, count = 0;
volatile char *token_temp[30];
volatile int toknum = 0;
int text_test()
{
char my_tokenised_string_buffer[255] = "Response\n\nCompany\nModel\nRevision: N01234567890\n\nOK";
const char delimiters[3] = "\n";
char *token = strtok(my_tokenised_string_buffer, delimiters);
token_temp[0] = malloc((1 + strlen(token)) * sizeof(char));
strcpy((char*) token_temp[0], token);
printf("first tokenised value = %s\n",token);
while (token != NULL)
{
++toknum ;
token = strtok(NULL, delimiters);
if (token != NULL) {
token_temp[toknum] = malloc((1 + strlen(token)) * sizeof(char));
strcpy((char*) token_temp[toknum], token);
} else {
token_temp[toknum] = NULL;
}
printf("toknum : %d\t",toknum);
printf("token id from inside tokenise loop : %s -> [%u]\n", token_temp[toknum], toknum);
}
printf("\n\n\n");
for(int i = 0; i < toknum;i++)
{
printf("token [%d] value in function out of tokenise = %s\n", i, token_temp[i]);
}
return 0;
}
int main()
{
text_test();
printf("\n\n\n");
for(int i = 0; i < toknum;i++)
{
printf("token [%d] value in main = %s\n",i, token_temp[i]);
}
return 0;
}
strtok()
is a confusing and error prone function. The pointer it returns points to the string that gets tokenized (which is modified for this purpose). strtok()
是一个令人困惑且容易出错的 function。它返回的指针指向被标记化的字符串(为此目的进行了修改)。 Storing these pointers to a global array, which by the way does not need to ne volatile
qualified, results in undefined behavior after the function returns as the array my_tokenised_string_buffer
is no longer valid.将这些指针存储到全局数组(顺便说一句,不需要 ne volatile
限定)会导致 function 返回后出现未定义的行为,因为数组my_tokenised_string_buffer
不再有效。
You should allocate copies of the tokens and take the destination array as an argument.您应该分配令牌的副本并将目标数组作为参数。
Here is a modified version:这是修改后的版本:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int text_test(char *token_temp[], int length) {
char my_tokenised_string_buffer[] = "Response\n\nCompany\nModel\nRevision: N01234567890\n\nOK";
const char delimiters[] = "\n";
char *token;
int toknum = 0;
token = strtok(my_tokenised_string_buffer, delimiters);
while (toknum + 1 < length && token != NULL) {
token_temp[toknum++]= strdup(token);
token = strtok(NULL, delimiters);
}
token_temp[toknum] = NULL; /* terminate the array with a null pointer */
return toknum; /* return the number of tokens */
}
int main() {
char *token_temp[30];
int array_length = sizeof(token_temp) / sizeof(*token_temp);
int toknum = 0;
toknum = text_test(token_temp, array_length);
/* print the tokens */
for (int i = 0; i < toknum; i++) {
printf("token [%d] value in main = %s\n", i, token_temp[i]);
}
/* free the tokens */
for (int i = 0; i < toknum; i++) {
free(token_temp[i]);
}
return 0;
}
You can use this code for solve your problem:您可以使用此代码来解决您的问题:
enter code here
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
//------------------------------------------------------------
int SpliteMessage(char* input , char sp , char token_temp[10][40])
{
int len = strlen(input);
int i,token_cnt=0,bcnt=0;
for (i=0 ; i<len ; i++)
{
if (input[i] == sp)
{
token_temp[token_cnt][bcnt] = 0;
token_cnt++;
bcnt=0;
}
else
{
token_temp[token_cnt][bcnt] = input[i];
bcnt++;
}
}
return token_cnt;
}
//----------------------------------------------------------------
int main()
{
char buffer[200] = "Response\n\nCompany\nModel\nRevision: N01234567890\n\nOK";
char t_temp[10][40];
int token_counter = SpliteMessage(buffer , '\n' , t_temp);
printf("\n--------------\n(Token Counter -> %i)\n",token_counter);
for (int i=0 ; i<token_counter ; i++)
printf("token[%i] from main: (%s) \n",i,t_temp[i]);
return 0;
}
regarding:关于:
token_temp[toknum]= token;
This just copies pointers, what is actually needed is to copy the data,.这只是复制指针,实际需要的是复制数据,。
Suggest:建议:
token_temp[ toknum ] = strdup( token );
which will create a copy of the data then place a pointer to that copy into the array这将创建数据的副本,然后将指向该副本的指针放入数组中
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