Diff: SW_String.cpp

Revision:

1:65bc379d8cd0

Parent:

0:6d899ce93ea0

Child:

2:c7a3039893cb

--- a/SW_String.cpp	Mon Apr 11 02:25:34 2016 +0000
+++ b/SW_String.cpp	Tue Apr 11 18:42:07 2017 +0000
@@ -2,6 +2,84 @@
 
 #include "SW_String.h"
 
+/// A more secure version of strcat
+///
+/// This function is like a wrapper on strcat, to first validate the concatination
+/// and then if all parameters appear good, it will call strcat. It will not
+/// permit overlapping source and destination.
+///
+/// If there is an error, no concatination is performed.
+///
+/// @note This has a different return value than the normal strcat.
+///
+/// @param[out] dst is a pointer to the start of the destination buffer (not necessarily
+///             where the next string will appear).
+/// @param[in] dstSize defines the size of the destination buffer.
+/// @param[in] src is a pointer to the source.
+///
+/// @returns 
+///     - 0 = no error
+///     - -1 = destination pointer invalid
+///     - -2 = source is too big to append into the destination
+///     - -3 = overlap between src and dst
+///
+int strcat_s(char * dst, size_t dstSize, const char * src) {
+    if (dst == NULL)
+        return -1;
+    if (src == NULL || *src == '\0')
+        return 0;       // done, that was easy.
+    if (src >= dst && src <= dst + dstSize)
+        return -3;
+    int dstLen = strlen(dst);
+    int srcLen = strlen(src);
+    if (src + srcLen >= dst && src + srcLen <= dst + dstSize)
+        return -3;
+    if (dstLen + srcLen > dstSize)
+        return -2;
+    strcat(dst, src);
+    return 0;
+}
+
+
+/// A more secure version of strcpy
+///
+/// This function is like a wrapper on strcpy, to first validate the concatination
+/// and then if all parameters appear good, it will call strcpy. It will not
+/// permit overlapping source and destination.
+///
+/// If there is an error, no copy is performed.
+///
+/// @note This has a different return value than the normal strcpy.
+///
+/// @param[out] dst is a pointer to the start of the destination buffer.
+/// @param[in] dstSize defines the size of the destination buffer.
+/// @param[in] src is a pointer to the source.
+///
+/// @returns 
+///     - 0 = no error
+///     - -1 = destination pointer invalid
+///     - -2 = source is too big to append into the destination
+///     - -3 = overlap between src and dst
+///
+int strcpy_s(char * dst, size_t dstSize, const char * src) {
+    if (dst == NULL)
+        return -1;
+    if (src == NULL || *src == '\0') {
+        *dst = '\0';
+        return 0;       // done, that was easy.
+    }
+    if (src >= dst && src <= dst + dstSize)
+        return -3;
+    int srcLen = strlen(src);
+    if (src + srcLen >= dst && src + srcLen <= dst + dstSize)
+        return -3;
+    if (srcLen > dstSize)
+        return -2;
+    strcpy(dst, src);
+    return 0;    
+}
+
+
 /// sw_tolower exists because not all compiler libraries have this function
 ///
 /// This takes a character and if it is upper-case, it converts it to