g_stpcpy: assertion 'dest != NULL' failed [gtk+]

Linusovic · 05-25-2017, 11:44 AM

I'm getting the this message when i'm trying to run this code ( in this function ).

GLib-CRITICAL **: g_stpcpy: assertion 'dest != NULL' failed

This is my functions code :

static void voltagelabelfunction(GtkWidget *widget, AllaVariabler *test){

char* str1;
char* str2;
char* str3;
str1 = "sssss";
str2 = "kkkk";
const gchar *text = gtk_entry_get_text(GTK_ENTRY(test->evoltage));
g_stpcpy (str3, text);
printf("str3 = %s\n", str3); //currently prints out str3 = (null)
}

This is inspired by the code below, I would like to merge two strings.

int main(int argc, char** argv) {

char* str1;
char* str2;
str1 = "sssss";
str2 = "kkkk";
char * str3 = (char *) malloc(1 +sizeof(char*) * (strlen(str1)+ strlen(str2)));
strcpy(str3, str1);
strcat(str3, str2);
printf("%s", str3);

return 0;
}

//Best regards Linusovic

ntubski · 05-25-2017, 12:50 PM

Quote:

Originally Posted by Linusovic

This is inspired by the code below, I would like to merge two strings.

You missed the part that allocates the destination buffer:

Code:

      char * str3 = (char *) malloc(1 +sizeof(char*) * (strlen(str1)+ strlen(str2)));

Linusovic · 05-25-2017, 01:16 PM

Quote:

Originally Posted by ntubski

You missed the part that allocates the destination buffer:

Code:

      char * str3 = (char *) malloc(1 +sizeof(char*) * (strlen(str1)+ strlen(str2)));

thx alot! it worked =)

ntubski · 05-25-2017, 01:29 PM

Code:

      char * str3 = (char *) malloc(1 +sizeof(char*) * (strlen(str1)+ strlen(str2)));

Although, looking at this again, it's allocating too much memory, that should be sizeof(char) which is the same as 1, which is redundant. The cast in front of malloc is also redundant, unless you're compiling C with a C++ compiler.

Code:

char * str3 = malloc(1 + strlen(str1) + strlen(str2));

Linusovic · 05-26-2017, 05:12 PM

Quote:

Originally Posted by ntubski

Code:

      char * str3 = (char *) malloc(1 +sizeof(char*) * (strlen(str1)+ strlen(str2)));

Although, looking at this again, it's allocating too much memory, that should be sizeof(char) which is the same as 1, which is redundant. The cast in front of malloc is also redundant, unless you're compiling C with a C++ compiler.

Code:

char * str3 = malloc(1 + strlen(str1) + strlen(str2));

Oh well i read somewhere that i needed the 1 + for the \0 end of the string. not sure if right or not. But also i'm compiling in c++ ^^

ntubski · 05-26-2017, 05:51 PM

Quote:

Originally Posted by Linusovic

Oh well i read somewhere that i needed the 1 + for the \0 end of the string.

That's correct. The extra part was the sizeof(char*).

Linusovic · 05-26-2017, 06:37 PM

Quote:

Originally Posted by ntubski

That's correct. The extra part was the sizeof(char*).

Ahh, makes sense. Didn't see the highlighted thing you did before!