[英]C - Using malloc, realloc and free. I get too many memory leaks, what's wrong?
So, my goal was to define a struct in which there is -所以,我的目标是定义一个结构,其中有 -
You can review my code, but I'm really having a hard time understanding what am I doing wrong -您可以查看我的代码,但我真的很难理解我做错了什么 -
I keep getting LOTS of memory leaks.我不断收到大量 memory 泄漏。 But I cannot understand why.但我不明白为什么。
Help and tips will be kindly appreciated.帮助和提示将不胜感激。
#include <stdio.h>
#include <stdlib.h>
struct {
char *command;
int arguments_count;
char **arguments;
} my_struct;
void cleanup(void);
int main() {
int i;
my_struct.command = (char *)malloc(6*sizeof(char));
my_struct.command = "print";
my_struct.arguments_count = 1;
my_struct.arguments = (char **)malloc(sizeof(char *));
my_struct.arguments[0] = "hello";
for(i = 1 ; i < 10; i++) {
my_struct.arguments = (char **)realloc(my_struct.arguments, sizeof(char *)*(i+1));
my_struct.arguments[i] = (char *)malloc(8*sizeof(char));
my_struct.arguments[i] = "hello";
my_struct.arguments_count++;
}
printf("Arguments count is: %d\n", my_struct.arguments_count);
printf("The arguments are:\n");
for(i = 0; i < 10; i++) {
printf("%s\n", my_struct.arguments[i]);
}
cleanup();
exit(0);
}
void cleanup(void) {
int i;
for(i = 0; i < 10; i++)
free(my_struct.arguments[i]);
free(my_struct.arguments);
free(my_struct.command);
}
strdup - The strdup() function returns a pointer to a new string which is a duplicate of the string s. strdup - strdup() function 返回一个指向新字符串的指针,该字符串是字符串 s 的副本。 Memory for the new string is obtained with malloc , and can be freed with free . Memory 的新字符串是用malloc获得的,并且可以用free释放。
my_struct.command = strdup("print");
my_struct.arguments_count = 1;
my_struct.arguments = (char**) malloc(sizeof(char*));
my_struct.arguments[0] = strdup("hello");
for (int i=1; i < 10; ++i) {
// if the number of args is known, allocate before entering the loop
my_struct.arguments = (char**) realloc(my_struct.arguments, sizeof(char*)*(i+1));
my_struct.arguments[i] = strdup("hello");
my_struct.arguments_count++;
}
// in your cleanup use the arguments_count var instead of the literal 10
for (int i=0; i < my_struct.arguments_count; ++i)
Your mistake was:你的错误是:
// allocate a memory block of 6 bytes
// assign the address of that block to command
my_struct.command = malloc(6);
// then you assigned the address of the string 'print' to command
// therefore the previous allocated block is lost -> mem leak
my_struct.command = "print";
// strdup does the following
return memcpy(malloc(strlen(str) + 1), str, strlen(str) + 1);
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