standard c library for escaping a string

If you were writing GPL stuff you might use http://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=lib/quotearg.c;hb=HEAD

There is no standard C library function for this.

When you use the declaration

char example[] = "first line\nsecond line: \"inner quotes\"";

the escape sequences will be interpreted and replaced by the compiler. You will have to "un-interpret" the characters that C escapes. Here's a quick-n-dirty example:

#include <stdio.h>
#include <ctype.h>

void print_unescaped(char* ptr, int len) {
    if (!ptr) return;
    for (int i = 0; i < len; i++, ptr++) {
        switch (*ptr) {
            case '\0': printf("\\0");  break;
            case '\a': printf("\\a");  break;
            case '\b': printf("\\b");  break;
            case '\f': printf("\\f");  break;
            case '\n': printf("\\n");  break;
            case '\r': printf("\\r");  break;
            case '\t': printf("\\t");  break;
            case '\v': printf("\\v");  break;
            case '\\': printf("\\\\"); break;
            case '\?': printf("\\\?"); break;
            case '\'': printf("\\\'"); break;
            case '\"': printf("\\\""); break;
            default:
                if (isprint(*ptr)) printf("%c",     *ptr);
                else               printf("\\%03o", *ptr);
        }
    }
}