confused with structs and pointers [closed] - c

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I am trying to fill a struct with strings.
struct person {
char *name
char age
};
int record_values(struct person *dude, const char *his_name, char his_age)
{
dude->name = malloc(strlen(his_name)*sizeof(char)); //Get space for name
strcpy(dude->name, his_name); //Set name
strcpy(dude->age, his_age); //Set age
}
However this doesn't work. Any help?

Answer 1

dude->name = malloc(strlen(his_name)*sizeof(char)); //Get space for name
strcpy(dude->name, his_name); //Set name
strcpy(dude->age, his_age); //Set age
Your first line doesn't allocate enough space. You need one byte for the string terminator.
Your last line calls strcpy, but his_age is not a string.

Answer 2

int record_values(struct person *dude, const char *his_name, char his_age)
{
dude->name = strdup(his_name); // Duplicate name
dude->age = his_age; // Set age (Simple assignment!)
}

Answer 3

Instead of giving pointers on what you should change in your code here an complete working example that hopefully shows the required differences. The code below first creates an struct person but when the function record_values() is called you'll see that it first has to check if dude-name is not pointing to an char array already. Not having this check would create a memory leak in your code and the previous dude->name will never be freed. Also it allocates one extra char space in the char array for the string terminator (strcpy will copy it as well). This will avoid overflow errors. The function returns nothing, so make it an void functions rather than an function returning an int. The value of dude->age is not a pointer to memory space, therefore strcpy should not be used but dude->age = his-age which copies the values of variables.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct person {
char *name;
char age;
};
struct person * record_alloc(const char *his_name, char his_age);
void record_values(struct person *dude, const char *his_name, char his_age);
void record_free(struct person * dude);
struct person * record_alloc(const char *his_name, char his_age){
struct person * dude;
dude = malloc(sizeof(struct person));
if (his_name != NULL){
record_values(dude, his_name, his_age);
} else {
dude->age = 0;
dude->name = NULL;
}
return dude;
}
void record_values(struct person *dude, const char *his_name, char his_age)
{
size_t nameSize;
if (dude->name)
free(dude->name);
nameSize = (strlen(his_name) + 1) * sizeof(char);
dude->name = malloc(nameSize);
strcpy(dude->name, his_name);
dude->age = his_age;
return;
}
void record_free(struct person * dude){
if (dude->name)
free(dude->name);
free(dude);
return;
}
int main(int argc, const char * argv[]) {
struct person * p;
// allocate and set values
p = record_alloc("John Smith", 32);
printf("%s is %i years old\n", p->name, p->age);
// set new values for p
record_values(p, "John Doe", 37);
printf("%s is %i years old\n", p->name, p->age);
// free p
record_free(p);
return 0;
}

Answer 4

You might prefer to use designated initializers:
#include <stdio.h>
#include <string.h>
typedef struct {
char *name;
char age;
} person;
int record_values(person *dude, const char *his_name, char his_age)
{
*dude = (person) {.name = strdup(his_name), .age = his_age};
}
int main()
{
person p;
record_values(&p, "bob", 27);
printf("Hello, I am %s and I am %d years old!\n", p.name, p.age);
return 0;
}
Hello, I am Bob and I am 27 years old!
Since strdup is not a part of c99 your compiler might generate warnings, to get rid of them you need to compile it with -std=gnu99:
gcc -std=gnu99 -o main *.c
Or use your own version of this, which might look like this:
#include <stdlib.h>
char * strdup(const char *in) {
char *out = malloc(sizeof(in) + 1);
int i;
for (i = 0; in[i] != '\0'; ++i)
out[i] = in[i];
return out;
}