how can i convert an int array into a string array

Question

I have an integer array:

int a[5]={5,21,456,1,3}

I need to store these number into char array so that the char array will have some thing like this:

char *s="52145613";

Is there any library function in c for this?

Solution 1

sprintf do what you need.

Little example

char str[128];
int i=0;
int index = 0;
for (i=0; i<5; i++)
   index += sprintf(&str[index], "%d", a[i]);

snprintf takes care of the str length

char str[128];
int i=0;
int index = 0;
for (i=0; i<5; i++)
   index += snprintf(&str[index], 128-index, "%d", a[i]);

Solution 2

What you need to do is to convert the integer values in a into character values in s leaving room for a null-terminating character. In your case a total of 9 characters. sprintf is the proper tool since vales exceed single digits:

#include <stdio.h>

int main(void)
{
    int a[5]={5,21,456,1,3};
    char s[9] = {0};
    int n = 0;

    for (int i = 0; i < 5; i++) {
        n += sprintf (&s[n], "%d", a[i]);
    }

    printf ("\n char* s = %s\n\n", s);

    return 0;
}

Output

$ ./bin/sprintf

 char* s = 52145613

Solution 3

Tried to go for a more readable approach even though the other answers are more efficient in terms of memory and instructions.

Tested it here.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void get_me_a_string(int * int_array, int array_size, char * output_string, int output_string_max_size)
{
    if(!int_array || !output_string)
        return;

    char * aux_string = NULL;

    //Depending on the compiler int is 2-byte or 4 byte.
    //Meaning INT_MAX will be at most 2147483647 (10 characters + 1 '\0').
    aux_string = (char *) malloc(11);
    if(!aux_string)
        return;

    int i;
    int current_array_size = 0;
    for(i = 0; i < array_size; i++)
    {
        sprintf(aux_string, "%d", int_array[i]);
        current_array_size += strlen(aux_string);
        if(current_array_size < output_string_max_size)
            strcat(output_string, aux_string);
        else
            break;
    }

    free(aux_string);
}

int main(void) {
    int a[5]={5,21,456,1,3};

    int string_max_size = 256;
    char * string_from_array = NULL;

    string_from_array  = (char *) malloc(string_max_size);

    if(NULL == string_from_array)
    {
        printf("Memory allocation failed. Exiting...");
        return 1;
    }

    memset(string_from_array, 0, string_max_size);
    get_me_a_string(a, 5, string_from_array, string_max_size);

    printf(string_from_array);

    free(string_from_array);
    return 0;
}

Solution 4

You can search for sprintf()/ snprintf() which can get the job done for you.

From the man page,

int sprintf(char *str, const char *format, ...); int snprintf(char *str, size_t size, const char *format, ...);

The functions in the printf() family produce output according to a format as described below....[...]...

sprintf(), snprintf(), vsprintf() and vsnprintf() write to the character string str.

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Comments

[David C. Rankin]

Got it -- no coffee yet - nuking ans.

[LPs]

@WoodrowBarlow Yes, I edited

[scai]

Beware that snprintf() returns a negative value in case of errors. Adding this value to index will be wrong.

[Fremzy]

This doesn't work if number of digits in resulting string is > 128

[Fremzy]

This can be further extended by making string_max_size dynamic , string_max_size = sizeof(a) / sizeof(a[0]*11;