将 char* 作为参数传递时出现分段错误 - c

Question

I'm having problems when I try to pass a char* as an argument, my code is like that:

int main(int argc, char** argv ) {
    if(argc > 1) {
        //not sure if I need this..
        char* base = malloc(strlen(argv[1]) + 1);
        strcpy(base, argv[1]);
        base[strlen(argv[1])] = '\0';

        printf("base is %s\n", base); //does it right

        testFunction(base);

        return 0;
    } else {
        //do something
    }
};

void testFunction(char* base) {
    //do things
    anotherFunction(base);
};

void anotherFunction(char* base) {
    char* command = malloc(52);
    command = "cp .tmp.db ";
    printf("Command before cat %s, base is   %s\n", command, base);
    strcat(command, base); //Segmentation fault
    printf("Command I need %s\n", command);
    //more things
}

I'm running it with ./program base.db , and output is like that:

base is base.db
Command before cat cp .tmp.db, base is  base.db

And then it just fails: Segmentation fault. I'm sure this is the line which is crashing because I run it with gdb, but I'm not sure what I'm doing wrong. I also tried to print base[i], with a for loop, but it has the same effect. I looked up other questions, but I can't solve this.

I know I should see if malloc was successful, I'll add it latter, I want to solve this first.

Answer 1

When you do the following

char* command = malloc(52);  //this memory is wasted
command = "cp .tmp.db ";    //this is string constant, and is kept in read only memory

Later, here

strcat(command,base);

You are trying to concat to the read only memory.

---

To correct this, use strcpy()

char* command = malloc(52);
strcpy(command, "cp .tmp.db ");

Answer 2

command = "cp .tmp.db "; should be strcpy(command, "cp .tmp.db ");

Answer 3

strcat appends copy of source string to the destination string, so destination should have enough of memory.

You allocated memory for the command variable, but then assigned literal value to it, so command stores pointer to the read only memory.

Modify your code like this:

char* command = (char*)calloc(128, sizeof(char));
strcpy(command, "cp .tmp.db ");
printf("Command before cat %s, base is   %s\n",command,base);
strcat(command,base);
printf("Command I need %s\n",command);