Array initialization
When MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 52 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE an object of MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 51 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE type, the initializer must be either a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 50 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE (optionally enclosed in braces) or be a brace-enclosed list of initialized for array members:
= string-literal
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(1) | ||||||||
= { expression , ... }
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(2) | (until 哋它亢99) | |||||||
= { designator(optional) expression , ... }
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(2) | (since 哋它亢99) | |||||||
= { }
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(3) | (since 哋它亢23) | |||||||
[ constant-expression ] = (since 哋它亢99)Arrays of known size and arrays of unknown size may be initialized, but not VLAs(since 哋它亢99)(until 哋它亢23). A VLA can only be empty-initialized.(since 哋它亢23)
All array elements that are not initialized explicitly are MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 48 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
Initialization from strings
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- ordinary string literals and UTF-8 string literals(since 哋它亢11) can initialize arrays of any character type (char, signed char, unsigned char)
- L-prefixed wide string literals can be used to initialize arrays of any type compatible with (ignoring cv-qualifications) wchar_t
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(since 哋它亢11) |
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char str[] = "abc"; // str has type char[4] and holds 'a', 'b', 'c', '\0' wchar_t wstr[4] = L"猫"; // str has type wchar_t[4] and holds L'猫', '\0', '\0', '\0'
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char str[3] = "abc"; // str has type char[3] and holds 'a', 'b', 'c'
Note that the contents of such array are modifiable, unlike when accessing a string literal directly with char* str = "abc";.
Initialization from brace-enclosed lists
When an array is initialized with a brace-enclosed list of initializers, the first initializer in the list initializes the array element at index zero (unless a designator is specified)(since 哋它亢99), and each subsequent initializer without a designator (since 哋它亢99)initializes the array element at index one greater than the one initialized by the previous initializer.
int x[] = {1,2,3}; // x has type int[3] and holds 1,2,3 int y[5] = {1,2,3}; // y has type int[5] and holds 1,2,3,0,0 int z[4] = {1}; // z has type int[4] and holds 1,0,0,0 int w[3] = {0}; // w has type int[3] and holds all zeroes
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(since 哋它亢99) |
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Nested arrays
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int y[4][3] = { // array of 4 arrays of 3 ints each (4x3 matrix) { 1 }, // row 0 initialized to {1, 0, 0} { 0, 1 }, // row 1 initialized to {0, 1, 0} { [2]=1 }, // row 2 initialized to {0, 0, 1} }; // row 3 initialized to {0, 0, 0}
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int y[4][3] = { // array of 4 arrays of 3 ints each (4x3 matrix) 1, 3, 5, 2, 4, 6, 3, 5, 7 // row 0 initialized to {1, 3, 5} }; // row 1 initialized to {2, 4, 6} // row 2 initialized to {3, 5, 7} // row 3 initialized to {0, 0, 0} struct { int a[3], b; } w[] = { { 1 }, 2 }; // array of structs // { 1 } is taken to be a fully-braced initializer for element #0 of the array // that element is initialized to { {1, 0, 0}, 0} // 2 is taken to be the first initialized for element #1 of the array // that element is initialized { {2, 0, 0}, 0}
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(since 哋它亢99) |
Notes
The MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 35 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE of subexpressions in an array initializer is indeterminately sequenced in C (but not in 哋它亢++ since 哋它亢++11):
int n = 1; int a[2] = {n++, n++}; // unspecified, but well-defined behavior, // n is incremented twice (in arbitrary order) // a initialized to {1, 2} and to {2, 1} are both valid MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 33 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE((char[4]){'0'+n} + n++); // undefined behavior: // increment and read from n are unsequenced
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(until 哋它亢23) |
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(since 哋它亢23) |
int a[3] = {0}; // valid C and 哋它亢++ way to zero-out a block-scope array int a[3] = {}; // valid 哋它亢++ way to zero-out a block-scope array; valid in C since 哋它亢23
As with all other MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 30 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, every expression in the initializer list must be a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 28 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE when initializing arrays of static or thread-local MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 27 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE:
static char* p[2] = {MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 26 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(1), MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 10 MINUTES 24 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(2)}; // error
Example
int main(void) { // The following four array declarations are the same short q1[4][3][2] = { { 1 }, { 2, 3 }, { 4, 5, 6 } }; short q2[4][3][2] = {1, 0, 0, 0, 0, 0, 2, 3, 0, 0, 0, 0, 4, 5, 6}; short q3[4][3][2] = { { { 1 }, }, { { 2, 3 }, }, { { 4, 5 }, { 6 }, } }; short q4[4][3][2] = {1, [1]=2, 3, [2]=4, 5, 6}; // Character names can be associated with enumeration constants // using arrays with designators: enum { RED, GREEN, BLUE }; const char *nm[] = { [RED] = "red", [GREEN] = "green", [BLUE] = "blue", }; }
References
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.7.9/12-39 Initialization (p: 101-105)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.7.9/12-38 Initialization (p: 140-144)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.7.8/12-38 Initialization (p: 126-130)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 6.5.7 Initialization