[英]C program malloc with array of strings
At the beginning of a program I need to dynamically allocate memory for an unknown number of strings with unknown number of size to later manipulate with. 在程序开始时,我需要为未知数量的字符串(大小未知)动态分配内存,以便以后使用。 To get the number of strings from a user I have:
要获得用户的字符串数,我需要:
int main(int argc, char *argv[]){
int number = atoi(argv[1]);
So far so good. 到现在为止还挺好。 "number" now holds holds the number that the user inputted on the command line for executing the code.
现在,“ number”保存着用户在命令行上输入的用于执行代码的数字。 Now here comes the part I don't quite understand.
现在是我不太了解的部分。 I now need to dynamically store the lengths of the strings as well as the contents of the strings.
现在,我需要动态存储字符串的长度以及字符串的内容。 For example, I want the program to function like this:
例如,我希望程序运行如下:
Enter the length of string 1: 5
Please enter string 1: hello
Enter the length of string 2: ...
For this I recognize that I will have to create an array of strings. 为此,我认识到必须创建一个字符串数组。 However, I can't quite understand the concept of pointers to pointers and what not.
但是,我不太了解指针的概念,而没有。 What I would like is perhaps a simplification of how this gets accomplished?
我想要的可能是如何简化此过程?
You know from the start you will have number
strings to store so you will need an array of size number
to store a pointer to each string. 您从一开始就知道要存储
number
字符串,因此需要一个大小为number
的数组来存储指向每个字符串的指针。
You can use malloc
to dynamically allocate enough memory for number
char pointers: 您可以使用
malloc
为number
char指针动态分配足够的内存:
char** strings = malloc(number * sizeof(char*));
Now you can loop number
times and allocate each string dynamically: 现在,您可以循环
number
次数和动态分配每个字符串:
for (int i = 0; i < number; i++) {
// Get length of string
printf("Enter the length of string %d: ", i);
int length = 0;
scanf("%d", &length);
// Clear stdin for next input
int c = getchar(); while (c != '\n' && c != EOF) c = getchar();
// Allocate "length" characters and read in string
printf("Please enter string %d: ", i);
strings[i] = malloc(length * sizeof(char));
fgets(strings[i], length, stdin);
}
Since you want to save both the length and the string, I'll suggest that you put them together in a struct. 既然你要保存的长度和字符串,我会建议你把它们放在一起的结构。 Like
喜欢
struct string
{
int length;
char* str;
};
Now you can dynamically create an array of this struct and dynamically assign memory for the individual strings. 现在,您可以动态创建此结构的数组,并为各个字符串动态分配内存。
Something like: 就像是:
#include <stdio.h>
#include <stdlib.h>
struct string
{
int length;
char* str;
};
int main(void) {
int i;
char tmp[128];
int number = 3;
struct string* strings = malloc(number * sizeof *strings);
// read the input
for (i=0; i<number; ++i)
{
printf("length?\n");
if (fgets(tmp, sizeof tmp, stdin) == NULL)
{
printf("error 1");
exit(1);
}
int length;
if (sscanf(tmp, "%d", &length) != 1)
{
printf("error 2");
exit(1);
}
strings[i].length = length;
strings[i].str = calloc(length + 2, 1);
printf("string?\n");
if (fgets(strings[i].str, length + 2, stdin) == NULL)
{
printf("error 3");
exit(1);
}
if (strings[i].str[length] != '\n')
{
printf("error 4");
exit(1);
}
strings[i].str[length] = '\0';
}
// print the strings
for (i=0; i<number; ++i)
{
printf("len=%d str=%s\n", strings[i].length, strings[i].str);
}
// Clean up, i.e. free the memory allocated
for (i=0; i<number; ++i)
{
free(strings[i].str);
}
free(strings);
return 0;
}
Note : You should also check that all malloc
/ calloc
are succesful, ie doesn't return NULL. 注意 :您还应该检查所有
malloc
/ calloc
是否成功,即不返回NULL。 For clarity I skipped that. 为了清楚起见,我略过了。
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