Is there a neat way to do strdup() followed by strcat()?

问题

Say I wanted to duplicate a string then concatenate a value to it.

Using stl std::string, it's:

string s = "hello" ;
string s2 = s + " there" ; // effectively dup/cat

in C:

char* s = "hello" ;
char* s2 = strdup( s ) ; 
strcat( s2, " there" ) ; // s2 is too short for this operation

The only way I know to do this in C is:

char* s = "hello" ;
char* s2=(char*)malloc( strlen(s) + strlen( " there" ) + 1 ) ; // allocate enough space
strcpy( s2, s ) ;
strcat( s2, " there" ) ;

Is there a more elegant way to do this in C?

回答1:

You could make one:

char* strcat_copy(const char *str1, const char *str2) {
    int str1_len, str2_len;
    char *new_str;

    /* null check */

    str1_len = strlen(str1);
    str2_len = strlen(str2);

    new_str = malloc(str1_len + str2_len + 1);

    /* null check */

    memcpy(new_str, str1, str1_len);
    memcpy(new_str + str1_len, str2, str2_len + 1);

    return new_str;
}

回答2:

Not really. C simply doesn't have a good string management framework like C++ does. Using malloc(), strcpy() and strcat() like you have shown is about as close as you can get to what you are asking for.

回答3:

You could use a library like GLib and then use its string type:

GString * g_string_append (GString *string, const gchar *val);

Adds a string onto the end of a GString, expanding it if necessary.

回答4:

A GNU extension is asprintf() that allocates the required buffer:

char* s2;
if (-1 != asprintf(&s2, "%s%s", "hello", "there")
{
    free(s2);
}

回答5:

Inspired by nightcracker, I also thought of

// writes s1 and s2 into a new string and returns it
char* catcpy( char* s1, char* s2 )
{
    char* res = (char*)malloc( strlen(s1)+strlen(s2)+1 ) ;

    // A:
    sprintf( res, "%s%s", s1, s2 ) ;
    return res ;

    // OR B:
    *res=0 ; // write the null terminator first
    strcat( res, s1 ) ;
    strcat( res, s2 ) ;
    return res ;
}

来源：https://stackoverflow.com/questions/12591074/is-there-a-neat-way-to-do-strdup-followed-by-strcat

标签

c-strings