I want to add a string to char pointer, how can i do?
For example:
char pointer is char * process_name; and i have an char array named second. It contains several chars.
I want to copy second to process_name.
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4 Answers
If you know the size of the buffer to which process_name points, you can use strncpy().
char * strncpy ( char * destination, const char * source, size_t num );
For example:
strncpy( process_name, second, process_name_size );
process_name[ process_name_size - 1 ] = '\0';
5 Comments
Ömer Faruk AK
can i get this with strlen(second)?
Andy Thomas
@Omer - you can get the size of second with strlen -- but you'll need a different method to get the size of the buffer pointed to by process_name. Typically either you're creating the buffer or being given the buffer; in the former case you know the size, and in the latter you can demand both the address and the size.
Andy Thomas
@BigMike - you caught me while I was still editing. But it's a good point -- I always just add it at the end of the buffer, which is harmless if strncpy wrote it, and necessary otherwise. :)
BigMike
@AndyThomas-Cramer: don't worry, I think that every seasoned C programmer adds the '\0' automatically without even thinking about it, so it was just for completeness of information (hope to have said it properly) :D. +1 for the '\0' in the sample. Regards.
Ömer Faruk AK
I solve my result like this, process_name = strdup(second); this works... =)
You can use 'strcat' or 'strncat' to concatenate two strings. But your process_name buffer has to be big enough to contain both strings. strcat will handle the \0-bytes for you but i'd still suggest you use strncat with fixed length.
char *strcat(char *restrict s1, const char *restrict s2);
char *strncat(char *restrict s1, const char *restrict s2, size_t n);
Example usage would be:
process_name = realloc(process_name, strlen(process_name) + strlen(second));
strncat(process_name, second, strlen(second));
This might not be the best example but it should show the general direction.
Comments
Strictly speaking, you cannot 'add a string' to a char pointer.
You can add a string to a buffer pointed to by a char pointer IF there is sufficient allocated space in the buffer (plus one for the terminating '\0') using a standard library call such as strncpy() [depends on your precise requirements, insert versus append etc].
2 Comments
m0skit0
AFAIK strncpy() will erase the original buffer. If he wants to ADD (append) a string, he should use strcat().
Mitch Wheat
I was assumming poster wants to add from a position onwards.
I resolve this problem with strdup() function.